netfilter: nft_reject: unify reject init and dump into nft_reject

[ Upstream commit 312ca575 ]

Bridge family is using the same static init and dump function as inet.

This patch removes duplicate code unifying these functions body into
nft_reject.c so they can be reused in the rest of families supporting
reject verdict.

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Stable-dep-of: 91a79b79 ("netfilter: nf_reject: don't leak dst refcount for loopback packets")
Signed-off-by: Sasha Levin <sashal@kernel.org>