netfilter: nf_tables: initialize registers in nft_do_chain()

netfilter: nf_tables: initialize registers in nft_do_chain()

Initialize registers to avoid stack leak into userspace.

Fixes: 96518518cc41 ("netfilter: add nftables")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
CVE-2022-1016
(cherry picked from commit 4c905f6740a365464e91467aa50916555b28213d)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>