Introduce gsm_lchans_name() for human readable lchan state name

Also, use this new function to dump lchan state on VTY and to
improve readability of RSL log messages.
diff --git a/openbsc/src/vty_interface.c b/openbsc/src/vty_interface.c
index 59865d5..22284d8 100644
--- a/openbsc/src/vty_interface.c
+++ b/openbsc/src/vty_interface.c
@@ -571,7 +571,8 @@
 		lchan->nr, lchan->ts->nr, lchan->ts->trx->nr, 
 		lchan->ts->trx->bts->nr, gsm_lchant_name(lchan->type),
 		VTY_NEWLINE);
-	vty_out(vty, "  Use Count: %u%s", lchan->use_count, VTY_NEWLINE);
+	vty_out(vty, "  Use Count: %u, State: %s%s", lchan->use_count,
+		gsm_lchans_name(lchan->state), VTY_NEWLINE);
 	vty_out(vty, "  BS Power: %u dBm, MS Power: %u dBm%s",
 		lchan->ts->trx->nominal_power - lchan->ts->trx->max_power_red
 		- lchan->bs_power*2,