libosmo-mgcp-client: extend the mgcp_client for MGW pooling

At the moment the MGCP Client only supports one MGW per application.
Depending on the requirements of the application one MGW might not offer
the performance needed. Lets add support for an MGCP Client pool that is
backward compatible to existing applications.

Change-Id: Icaaba0e470e916eefddfee750b83f5f65291a6b0
Related: SYS#5091
diff --git a/include/osmocom/mgcp_client/mgcp_client_fsm.h b/include/osmocom/mgcp_client/mgcp_client_fsm.h
index e315753..ade4f49 100644
--- a/include/osmocom/mgcp_client/mgcp_client_fsm.h
+++ b/include/osmocom/mgcp_client/mgcp_client_fsm.h
@@ -69,5 +69,6 @@
 void mgcp_conn_delete(struct osmo_fsm_inst *fi);
 
 const char *mgcp_conn_get_ci(struct osmo_fsm_inst *fi);
+struct mgcp_client *mgcp_conn_get_client(struct osmo_fsm_inst *fi);
 
 const char *osmo_mgcpc_conn_peer_name(const struct mgcp_conn_peer *info);