freetdm: improve some isdn logging

         try to fool-proof the size of the read D channel buffer by not hard-coding it in 2 places

libs/freetdm/src/ftmod/ftmod_sangoma_isdn/ftmod_sangoma_isdn.c

@@ -391,7 +391,7 @@ static void *ftdm_sangoma_isdn_io_run(ftdm_thread_t *me, void *obj)
 			case FTDM_SUCCESS:
 				/* Check if there are any channels that have data available */
 				for (citer = ftdm_span_get_chan_iterator(span, chaniter); citer; citer = ftdm_iterator_next(citer)) {
-					len = 1000;
+					len = sizeof(data);
 					ftdmchan = ftdm_iterator_current(citer);
 					if (FTDM_IS_VOICE_CHANNEL(ftdmchan)) {
 						if (ftdm_test_flag(ftdmchan, FTDM_CHANNEL_RX_DISABLED)) {

libs/freetdm/src/ftmod/ftmod_sangoma_isdn/ftmod_sangoma_isdn_stack_out.c

@@ -483,7 +483,8 @@ void sngisdn_snd_data(ftdm_channel_t *dchan, uint8_t *data, ftdm_size_t len)
 	sngisdn_span_data_t *signal_data = (sngisdn_span_data_t*) dchan->span->signal_data;
 
 	if (len > sizeof(l1_frame.data)) {
-		ftdm_assert(FTDM_FALSE, "Received frame exceeding max size\n");
+		ftdm_log_chan(dchan, FTDM_LOG_ERROR, "Received frame of %"FTDM_SIZE_FMT" bytes, exceeding max size of %"FTDM_SIZE_FMT" bytes\n", 
+				len, sizeof(l1_frame.data));
 		return;
 	}