Build fix: need to add -lpi_rpc to build ovs-vswitchd

[dreibh]

P4-OvS fails to build, due to missing inclusion of the pi_rpc library, as reported in #4 ,
leading to undefined symbols:
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_node_modify' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_grp_create'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_activate_mbr' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_update_device_end'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_session_init' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_table_entry_modify_wkey'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_counter_read' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_create'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_meter_read_direct' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_destroy'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_learn_config_set' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_remove_mbr'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_add_mbr' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_mbr_modify'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_grp_delete' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_deactivate_mbr'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_fetch' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_meter_set'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_session_init' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_port_status_get'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_init' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_counter_write_direct'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_table_entries_fetch_one' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_mbr_fetch'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_remove_device' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_entries_fetch_done'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_batch_end' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_learn_msg_done'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_session_cleanup' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_batch_begin'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_counter_write' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_table_entries_fetch_wkey'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_counter_read_direct' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_learn_msg_ack'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_node_delete' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_meter_read'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_entries_fetch' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_table_entry_modify'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_mbr_delete' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_api_support'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_node_create' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_meter_set_direct'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_session_cleanup' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_table_entry_get_remaining_ttl'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_clone_session_reset' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_grp_detach_node'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_delete' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_packetout_send'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_grp_set_mbrs' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_clone_session_set'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_counter_hw_sync' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_act_prof_mbr_create'
/usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_mc_grp_attach_node' /usr/bin/ld: /usr/lib/libpi.so: undefined reference to _pi_table_idle_timeout_config_set'

This pull request adds the missing pi_rpc library to the automake.mk to fix the build issue.

[osinstom]

Hi, thanks for the pull request. I see that Travis CI build is failing with the above change. It seems that pi_rpc library is not properly installed on the CI environment and cannot be found.

Could you tell me how did you build the PI library?

Moreover, I would suggest to include the additional library (pi_rpc) in p4rt/automake.mk