cls_flower: pass offload flags to tc_cls_common_offload_init()

Pass offload flags to the new implementation of
tc_cls_common_offload_init().  Extack will now only
be set if user requested skip_sw.

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>