netfilter: nf_tables: validate registers coming from userspace.

[ 6e1acfa387b9ff82cfc7db8cc3b6959221a95851 ]

Bail out in case userspace uses unsupported registers.

Fixes: 49499c3e ("netfilter: nf_tables: switch registers to 32 bit addressing")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>