Kernels that do not have f6b10209 ("virtio-net: switch to use
build_skb() for small buffer") will have an extra call to skb_to_sgvec
that is not handled by e2fcad58 ("virtio_net: check return value of
skb_to_sgvec always"). Since the former does not appear to be stable
material, just fix the call up directly.

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