ftmod_misdn: Discard incoming audio data if b-channel is not active

Silences the "Device or resource busy" error messages caused by the RX pipe
filling up.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>

libs/freetdm/src/ftmod/ftmod_misdn/ftmod_misdn.c

@@ -2265,6 +2265,8 @@ static ftdm_status_t handle_b_channel_event(ftdm_channel_t *chan)
 		int datalen = retval - MISDN_HEADER_LEN;
 		char *data  = buf    + MISDN_HEADER_LEN;
 
+		/* Discard incoming audio if not active */
+		if (!priv->active) {
 			/* Convert audio data */
 			misdn_convert_audio_bits(data, datalen);
 
@@ -2278,6 +2280,7 @@ static ftdm_status_t handle_b_channel_event(ftdm_channel_t *chan)
 					retval, datalen);
 				return FTDM_FAIL;
 			}
+		}
 
 		/* Get receive buffer usage */
 		if (ioctl(priv->tx_audio_pipe_out, FIONREAD, &retval) < 0) {