udp: Convey transmit path errors to the caller.

The transport layer's functional interface foresees having error codes
percolate back up to the caller.  However, up until now, the udp module
simply returned -1 for any error.  This patch lets the code return the
specific error instead.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

udp.c

@@ -256,7 +256,7 @@ static int udp_send(struct transport *t, struct fdarray *fda,
 	cnt = sendto(fd, buf, len, 0, &addr->sa, sizeof(addr->sin));
 	if (cnt < 1) {
 		pr_err("sendto failed: %m");
-		return cnt;
+		return -errno;
 	}
 	/*
 	 * Get the time stamp right away.