netfilter: nf_tables: out-of-bound check in chain blob

[ Upstream commit 08e42a0d ]

Add current size of rule expressions to the boundary check.

Fixes: 2c865a8a ("netfilter: nf_tables: add rule blob layout")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>