misc: Print the payload that is not known

Print the payload type that is not handled as this allows one to
look it up in the specification.
diff --git a/src/gprs_rlcmac.cpp b/src/gprs_rlcmac.cpp
index 4f39bee..c6a91d8 100644
--- a/src/gprs_rlcmac.cpp
+++ b/src/gprs_rlcmac.cpp
@@ -1174,7 +1174,7 @@
 		LOGP(DRLCMAC, LOGL_NOTICE, "GPRS_RLCMAC_CONTROL_BLOCK_OPT block payload is not supported.\n");
 		break;
 	default:
-		LOGP(DRLCMAC, LOGL_NOTICE, "Unknown RLCMAC block payload.\n");
+		LOGP(DRLCMAC, LOGL_NOTICE, "Unknown RLCMAC block payload(%u).\n", payload);
 		rc = -EINVAL;
 	}