fw4: disable "flow_offloading_hw" option for now

fw4: disable "flow_offloading_hw" option for now

Currently there does not appear to exist any kernel side nft flowtable
implementation that supports hardware flow offloading.

Attempting to upload a ruleset containing a flowtable declaration with
the hardware offloading flag set will fail with a generic EOPNOTSUPP
error.

Since there is neither a graceful recovery (e.g. continue without
hardware flow offloading) nor any possibility to probe kernel side
support from userspace, disable the facility entirely for now.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>