Do not log errors when recvfrom() returns EAGAIN or EINTR.

Although we select() before we call recvfrom(), it sometimes happens that
select() tells us we can read but a subsequent read fails anyway. This is
harmless.

src/net_packet.c

@@ -552,6 +552,7 @@ void handle_incoming_vpn_data(int sock)
 	pkt.len = recvfrom(sock, (char *) &pkt.seqno, MAXSIZE, 0, &from.sa, &fromlen);
 
 	if(pkt.len < 0) {
+		if(errno != EAGAIN && errno != EINTR)
 			logger(LOG_ERR, _("Receiving packet failed: %s"), strerror(errno));
 		return;
 	}