Re-try the writing on EAGAIN.

As the UDP sockets were moved to non blocking, sendto() may generate EAGAIN if the prev write operation was not yet completed by the stack.

net/proto_udp/proto_udp.c

@@ -213,7 +213,7 @@ static int proto_udp_send(struct socket_info* source,
 	if (n==-1){
 		LM_ERR("sendto(sock,%p,%d,0,%p,%d): %s(%d)\n", buf,len,to,tolen,
 				strerror(errno),errno);
-		if (errno==EINTR) goto again;
+		if (errno==EINTR || errno==EAGAIN) goto again;
 		if (errno==EINVAL) {
 			LM_CRIT("invalid sendtoparameters\n"
 			"one possible reason is the server is bound to localhost and\n"