rspro_server: Add client_conn_by_slot()  API function

Change-Id: Ie2eefad358b45541cf90d0cacac2d03953f0c367
diff --git a/src/server/rspro_server.h b/src/server/rspro_server.h
index 1703cb5..af84c18 100644
--- a/src/server/rspro_server.h
+++ b/src/server/rspro_server.h
@@ -56,5 +56,7 @@
 void rspro_server_destroy(struct rspro_server *srv);
 int event_fd_cb(struct osmo_fd *ofd, unsigned int what);
 
+struct rspro_client_conn *_client_conn_by_slot(struct rspro_server *srv, const struct client_slot *cslot);
+struct rspro_client_conn *client_conn_by_slot(struct rspro_server *srv, const struct client_slot *cslot);
 struct rspro_client_conn *_bankd_conn_by_id(struct rspro_server *srv, uint16_t bank_id);
 struct rspro_client_conn *bankd_conn_by_id(struct rspro_server *srv, uint16_t bank_id);