Handle UDP packets with unknown source addresses properly.

Probably due to a merge, the try_harder() function had duplicated the
rate-limiting code for detecting the sender node based on the HMAC of the
packet. This prevented this detection from running at all. The function is now
identical again to that in the 1.0 branch.

src/net_packet.c

@@ -570,11 +570,6 @@ static node_t *try_harder(const sockaddr_t *from, const vpn_packet_t *pkt) {
 	static time_t last_hard_try = 0;
 	time_t now = time(NULL);
 
-	if(last_hard_try == now)
-		return NULL;
-	else
-		last_hard_try = now;
-
 	for(node = edge_weight_tree->head; node; node = node->next) {
 		e = node->data;