cls_bpf: remove gen_flags from bpf_offload

cls_bpf now guarantees that only device-bound programs are
allowed with skip_sw.  The drivers no longer pay attention to
flags on filter load, therefore the bpf_offload member can be
removed.  If flags are needed again they should probably be
added to struct tc_cls_common_offload instead.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>