net/sched: act_mirred: Add new tc_action_ops get_dev()

Adding support to a new tc_action_ops.
get_dev is a general option which allows to get the underline
device when trying to offload a tc rule.

In case of mirred action the returned device is the mirred (egress)
device.

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