net/mlx5: support e-switch flow count action

net/mlx5: support e-switch flow count action

This commit adds support for configuring flows destined to the mlx5
eswitch with 'count' action and for querying these counts at runtime.

Each flow rule configured by the mlx5 driver is implicitly assigned
with flow counters. These counters can be retrieved when querying
the flow rule via Netlink, they can be found in each flow action
section of the reply. Hence, supporting the 'count' action in the
flow configuration command is straight-forward. When transposing
the command to a tc Netlink message we just ignore it instead of
rejecting it.
In the 'flow query count' side, the command now uses tc Netlink
query command in order to retrieve the values of the flow counters.

Signed-off-by: Moti Haimovsky <motih@mellanox.com>