bsc_api: Move gsm48_rcvmsg into the BSC API and dispatch.

The next step in the way to the BSC API. We have a clear a
new connection was opened signal now... and the MSC could
use it...
diff --git a/openbsc/src/gsm_04_11.c b/openbsc/src/gsm_04_11.c
index a9eee83..cb7cf85 100644
--- a/openbsc/src/gsm_04_11.c
+++ b/openbsc/src/gsm_04_11.c
@@ -913,7 +913,7 @@
 
 /* Entry point for incoming GSM48_PDISC_SMS from abis_rsl.c */
 int gsm0411_rcv_sms(struct gsm_subscriber_connection *conn,
-		    struct msgb *msg, u_int8_t link_id)
+		    struct msgb *msg)
 {
 	struct gsm48_hdr *gh = msgb_l3(msg);
 	u_int8_t msg_type = gh->msg_type;
@@ -940,7 +940,7 @@
 		trans->sms.cp_state = GSM411_CPS_IDLE;
 		trans->sms.rp_state = GSM411_RPS_IDLE;
 		trans->sms.is_mt = 0;
-		trans->sms.link_id = link_id;
+		trans->sms.link_id = UM_SAPI_SMS;
 
 		trans->conn = conn;
 		use_subscr_con(trans->conn);