netfilter: nftables: allow to update flowtable flags

stable inclusion
from stable-5.10.27
commit 186d8dc40a65f0248df2ed34292f1296158d0be4
bugzilla: 51493

--------------------------------

[ Upstream commit 7b35582c ]

Honor flowtable flags from the control update path. Disallow disabling
to toggle hardware offload support though.

Fixes: 8bb69f3b ("netfilter: nf_tables: add flowtable offload control plane")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by:   Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>