i40e: Add macvlan support on i40e

This patch enables macvlan offloads for i40e. The idea is to use
channels as macvlan interfaces. The channels are VSIs of
type VMDQ. When the first macvlan is created, the maximum number of
channels possible are created. From then on, as a macvlan interface
is created, a macvlan filter is added to these already created
channels (VSIs).

This patch utilizes subordinate device traffic classes to make queue
groups(channels) available for an upper device like a macvlan.

Steps to configure macvlan offloads:
1. ethtool -K ethx l2-fwd-offload on
2. ip link add link ethx name macvlan1 type macvlan
3. ip addr add <address> dev macvlan1
4. ip link set macvlan1 up

Signed-off-by: Harshitha Ramamurthy <harshitha.ramamurthy@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>