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/include/openbsc/gsm_04_08.h b/openbsc/include/openbsc/gsm_04_08.h
index 11bca54..3fbc35f 100644
--- a/openbsc/include/openbsc/gsm_04_08.h
+++ b/openbsc/include/openbsc/gsm_04_08.h
@@ -25,6 +25,7 @@
 /* config options controlling the behaviour of the lower leves */
 void gsm0408_allow_everyone(int allow);
 void gsm0408_clear_request(struct gsm_subscriber_connection *conn, uint32_t cause);
+int gsm0408_dispatch(struct gsm_subscriber_connection *conn, struct msgb *msg);
 
 int gsm0408_rcvmsg(struct msgb *msg, u_int8_t link_id);
 enum gsm_chan_t get_ctype_by_chreq(struct gsm_bts *bts, u_int8_t ra, int neci);