cls_u32: propagate extack to delete callback

Propagate extack on removal of offloaded filter.  Don't pass
extack from error paths.

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>