net/mlx5e: Introduce tc offload support

Extend ndo_setup_tc() to support ingress tc offloading. Will be used by
later patches to offload tc flower filter.

Feature is off by default and could be enabled by issuing:
 # ethtool  -K eth0 hw-tc-offload on

Offloads flow table is dynamically created when first filter is
added.
Rules are saved in a hash table that is maintained by the consumer (for
example - the flower offload in the next patch).
When last filter is removed and no filters exist in the hash table, the
offload flow table is destroyed.

Signed-off-by: Amir Vadai <amir@vadai.me>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>