xsk: do not return EMSGSIZE in copy mode for packets larger than MTU

This patch stops returning EMSGSIZE from sendmsg in copy mode when the
size of the packet is larger than the MTU. Just send it to the device
so that it will drop it as in zero-copy mode. This makes the error
reporting consistent between copy mode and zero-copy mode.

Fixes: 35fcde7f ("xsk: support for Tx")
Signed-off-by: NMagnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

net/xdp/xsk.c

@@ -233,15 +233,10 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
 		if (xskq_reserve_addr(xs->umem->cq))
 			goto out;
 
-		len = desc.len;
-		if (unlikely(len > xs->dev->mtu)) {
-			err = -EMSGSIZE;
-			goto out;
-		}
-
 		if (xs->queue_id >= xs->dev->real_num_tx_queues)
 			goto out;
 
+		len = desc.len;
 		skb = sock_alloc_send_skb(sk, len, 1, &err);
 		if (unlikely(!skb)) {
 			err = -EAGAIN;