netfilter: nft_fwd_netdev: validate family and chain type

commit 76a109fac206e158eb3c967af98c178cff738e6a upstream.

Make sure the forward action is only used from ingress.

Fixes: 39e6dea2 ("netfilter: nf_tables: add forward expression to the netdev family")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>