reschedule iface even when send fails

Not rescheduling can leave the iface as the next iface to expire
which will peg the CPU at 100% if sending continues to fail.  This
change logs the failure and reschedules like normal when the iface
failes to send an ra.

Conflicts:
	radvd.c

radvd.c

@@ -464,7 +464,7 @@ void timer_handler(void *data)
 	dlog(LOG_DEBUG, 4, "timer_handler called for %s", iface->Name);
 
 	if (send_ra_forall(iface, NULL) != 0) {
-		return;
+		dlog(LOG_DEBUG, 4, "send_ra_forall failed on interface %s", iface->Name);
 	}
 
 	next = rand_between(iface->MinRtrAdvInterval, iface->MaxRtrAdvInterval);