net: sched: cls_flower: move key/mask dumping into a separate function

Push key/mask dumping from fl_dump() into a separate function
fl_dump_key(), that will be reused for template dumping.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>