abis_rsl: inform user when expired channel requests get tossed

At the moment expired channel requests are dropped silently, however, it
might help to know when this happens - not only for debugging.

Change-Id: Ib49df551a4cd7d5652e85c8ce29ef132385d4ae4
Related: OS#4549
diff --git a/src/osmo-bsc/abis_rsl.c b/src/osmo-bsc/abis_rsl.c
index c0907c0..347be12 100644
--- a/src/osmo-bsc/abis_rsl.c
+++ b/src/osmo-bsc/abis_rsl.c
@@ -1384,10 +1384,14 @@
 	llist_for_each_entry_safe(rqd, rqd_tmp, &bts->chan_rqd_queue, entry) {
 		/* If the channel request is older than the radio link timeout we drop it. This also means that the
 		 * queue is under its overflow limit again. */
-		if (timestamp_current - rqd->timestamp > rlt)
+		if (timestamp_current - rqd->timestamp > rlt) {
+			LOG_BTS(bts, DRSL, LOGL_INFO, "CHAN RQD: tossing expired channel request"
+				"(ra=0x%02x, neci=0x%02x, chreq_reason=0x%02x)\n",
+				rqd->ref.ra, bts->network->neci, rqd->reason);
 			llist_del(&rqd->entry);
-		else
+		} else {
 			rqd_count++;
+		}
 	}
 
 	/* If we find more than 255 (256) unexpired channel requests in the queue it is very likely that there is a