nat: Logging improvement for the nat.

Print some more information, e.g. when a BSC is connected
and authenticated, print the SCCP ref number.
diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index 2ca28cc..9fb4f02 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -375,6 +375,7 @@
 			bsc->authenticated = 1;
 			bsc->lac = conf->lac;
 			bsc_del_timer(&bsc->id_timeout);
+			LOGP(DNAT, LOGL_NOTICE, "Authenticated bsc %d\n", bsc->lac);
 			break;
 		}
 	}
@@ -570,7 +571,7 @@
 		return -2;
 	}
 
-	LOGP(DNAT, LOGL_INFO, "Registered new BSC\n");
+	LOGP(DNAT, LOGL_NOTICE, "Registered new BSC\n");
 	llist_add(&bsc->list_entry, &nat->bsc_connections);
 	send_id_ack(bsc);
 	send_id_req(bsc);