nat: Keep track of the MSC handling the connection.

In the future we might have multiple MSCs connected
and need to dispatch it to the right one.

openbsc/include/openbsc/bsc_nat.h

@@ -120,6 +120,7 @@ struct sccp_connections {
 	struct llist_head list_entry;
 
 	struct bsc_connection *bsc;
+	struct bsc_msc_connection *msc_con;
 
 	struct sccp_source_reference real_ref;
 	struct sccp_source_reference patched_ref;

openbsc/src/nat/bsc_nat.c

@@ -703,6 +703,7 @@ static int forward_sccp_to_msc(struct bsc_connection *bsc, struct msgb *msg)
 			if (!create_sccp_src_ref(bsc, parsed))
 				goto exit2;
 			con = patch_sccp_src_ref_to_msc(msg, parsed, bsc);
+			con->msc_con = bsc->nat->msc_con;
 			con->con_type = con_type;
 			con_found = 1;
 			con_bsc = con->bsc;