net/mlx5e: Support DCBX CEE API

Add DCBX CEE API interface for ConnectX-4. Configurations are stored in
a temporary structure and are applied to the card's firmware when
the CEE's setall callback function is called.

Note:
  priority group in CEE is equivalent to traffic class in ConnectX-4
  hardware spec.

  bw allocation per priority in CEE is not supported because ConnectX-4
  only supports bw allocation per traffic class.

  user priority in CEE does not have an equivalent term in ConnectX-4.
  Therefore, user priority to priority mapping in CEE is not supported.

Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>