igb: Add support for adding offloaded clsflower filters

This allows filters added by tc-flower and specifying MAC addresses,
Ethernet types, and the VLAN priority field, to be offloaded to the
controller.

This reuses most of the infrastructure used by ethtool, but clsflower
filters are kept in a separated list, so they are invisible to
ethtool.

To setup clsflower offloading:

$ tc qdisc replace dev eth0 handle 100: parent root mqprio \
     	   	   num_tc 3 map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
		   queues 1@0 1@1 2@2 hw 0
(clsflower offloading depends on the netword driver to be configured
with multiple traffic classes, we use mqprio's 'num_tc' parameter to
set it to 3)

$ tc qdisc add dev eth0 ingress

Examples of filters:

$ tc filter add dev eth0 parent ffff: flower \
     	    dst_mac aa:aa:aa:aa:aa:aa \
	    hw_tc 2 skip_sw
(just a simple filter filtering for the destination MAC address and
steering that traffic to queue 2)

$ tc filter add dev enp2s0 parent ffff: proto 0x22f0 flower \
     	    src_mac cc:cc:cc:cc:cc:cc \
	    hw_tc 1 skip_sw
(as the i210 doesn't support steering traffic based on the source
address alone, we need to use another steering traffic, in this case
we are using the ethernet type (0x22f0) to steer traffic to queue 1)

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>