[wishlist] preserve docker etc soft bridge sw offload with hw offload enabled

[brada4]

Just derived from another accidental side effect of reducing scope of soft offloads in https://github.com/openwrt/firewall4/commit/e00958884416f59b273595f941d198de63acc1dd 2-3x throughput or 2-3x less cpu cycles for same data moved in and out of container if implemented.