netfilter: nft_reject: add reject verdict support for netdev

Adds support for reject from ingress hook in netdev family.
Both stacks ipv4 and ipv6.  With reject packets supporting ICMP
and TCP RST.

This ability is required in devices that need to REJECT legitimate
clients which traffic is forwarded from the ingress hook.

Joint work with Laura Garcia.

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>