netfilter: nf_tables: fully validate NFT_DATA_VALUE on store to data registers

[ Upstream commit 7931d32955e09d0a11b1fe0b6aac1bfa061c005c ]

register store validation for NFT_DATA_VALUE is conditional, however,
the datatype is always either NFT_DATA_VALUE or NFT_DATA_VERDICT. This
only requires a new helper function to infer the register type from the
set datatype so this conditional check can be removed. Otherwise,
pointer to chain object can be leaked through the registers.

Fixes: 96518518 ("netfilter: add nftables")
Reported-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 40188a25a9847dbeb7ec67517174a835a677752f)
[Vegard: fixed unrelated conflict due to missing commit
 9c22bd1ab442c552e9481f1157589362887a7f47 ("netfilter: nf_tables: defer
 gc run if previous batch is still pending").]
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>