virtio_net: check return value of skb_to_sgvec always

commit e2fcad58fd230f635a74e4e983c6f4ea893642d2 upstream.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>