ixgbe: enable l2 forwarding acceleration for macvlans

Now that l2 acceleration ops are in place from the prior patch,
enable ixgbe to take advantage of these operations.  Allow it to
allocate queues for a macvlan so that when we transmit a frame,
we can do the switching in hardware inside the ixgbe card, rather
than in software.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Andy Gospodarek <andy@greyhouse.net>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>