mgcp-client: Introduce APIs to manually select mgcp_client from pool

This will be used by osmo-bsc to implement MGW-pinning for specific BTS.
This is useful for instance to keep all BTS connections targeting the
same MGW in order to make use of Osmux trunking optimizations (AMR
payload of different calls filling same underlaying UDP packet).

Related: SYS#5987
Change-Id: I75ce3e04cd3f6d9cc20d7b4fc0f51083780786c8
diff --git a/TODO-RELEASE b/TODO-RELEASE
index c480ba0..5fe3d53 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -25,4 +25,5 @@
 #
 #library		what		description / commit summary line
 libosmo-netif           >1.2.0          OSMUX_DEFAULT_PORT, osmux_xfrm_output_*, osmux_xfrm_input_*
-libosmocore             >1.7.0          osmo_sockaddr_is_any()
\ No newline at end of file
+libosmocore             >1.7.0          osmo_sockaddr_is_any()
+libmgcp-client          NEW APIs        mgcp_client_pool_member_...()
\ No newline at end of file