sipreg: avoid sending un-REGISTER periodically
A periodic un-REGISTER should be done only if `fbregint` (fallback SIP server
registration interval) was set.
@@ -254,6 +254,8 @@ static void response_handler(int err, const struct sip_msg *msg, void *arg)
if (reg->fbregint)
tmr_start(&reg->tmr, reg->fbregint * 1000,
tmr_handler, reg);
+ else
+ tmr_cancel(&reg->tmr);
reg->resph(err, msg, reg->arg);
