osmo_msc: remove unused parameter from msc_dtap()

The parameter link_id in the function msc_dtap() is unused. Lets remove
it.

Change-Id: I7ba67b0cb514c91bc87a7b396ed3962b7a68e7da
diff --git a/src/libmsc/iucs.c b/src/libmsc/iucs.c
index a3092f8..95bbbee 100644
--- a/src/libmsc/iucs.c
+++ b/src/libmsc/iucs.c
@@ -173,7 +173,7 @@
 		uint8_t pdisc = gh->proto_discr & 0x0f;
 		OSMO_ASSERT(pdisc != GSM48_PDISC_RR);
 
-		msc_dtap(conn, ue_ctx->conn_id, msg);
+		msc_dtap(conn, msg);
 		rc = 0;
 	} else {
 		/* allocate a new connection */