netfilter: bridge: add reject support

So you can reject IPv4 and IPv6 packets from bridge tables. If the ether
proto is now known, default on dropping the packet instead.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --cc net/bridge/netfilter/Kconfig
Simple merge

diff --cc net/bridge/netfilter/Makefile
Simple merge

diff --cc net/bridge/netfilter/nft_reject_bridge.c
Simple merge