freetdm: fix queue full problem

- restore flushing queue when channel state goes to down

libs/freetdm/src/ftmod/ftmod_sangoma_ss7/ftmod_sangoma_ss7_main.c

@@ -1599,6 +1599,7 @@ ftdm_status_t ftdm_sangoma_ss7_process_state_change (ftdm_channel_t *ftdmchan)
 			ftdm_channel_t *close_chan = ftdmchan;
 			/* close the channel */
 			SS7_DEBUG_CHAN(ftdmchan,"FTDM Channel Close %s\n", "");
+			sngss7_flush_queue(sngss7_info->event_queue);
 			ftdm_channel_close (&close_chan);
 		}