net/sched: introduce Match-all classifier

The matchall classifier matches every packet and allows the user to apply
actions on it. This filter is very useful in usecases where every packet
should be matched, for example, packet mirroring (SPAN) can be setup very
easily using that filter.

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