netfilter: nftables: report EOPNOTSUPP on unsupported flowtable flags

stable inclusion
from stable-5.10.27
commit 4a741b4df032de7de45e709ead6d8e4f5ce8d20b
bugzilla: 51493

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

[ Upstream commit 7e6136f1 ]

Error was not set accordingly.

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>