netfilter: nft_flow_offload: missing netlink attribute policy

[ Upstream commit 14c41586 ]

The netlink attribute policy for NFTA_FLOW_TABLE_NAME is missing.

Fixes: a3c90f7a

 ("netfilter: nf_tables: flow offload expression")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>