netfilter: nf_flow_table_offload: Fix block setup as TC_SETUP_FT cmd

Set up block through TC_SETUP_FT command.

Fixes: c29f74e0 ("netfilter: nf_flow_table: hardware offload support")
Signed-off-by: wenxu <wenxu@ucloud.cn>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>