When jumbo frames are enabled, the Linux ixgbe physical function
driver will disable the virtual function's receive datapath by
default, and will enable it only if the virtual function negotiates
API version 1.1 (or higher) and explicitly selects an MTU.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Virtual functions use a mailbox to communicate with the physical
function driver: this covers functionality such as obtaining the MAC
address.

Signed-off-by: Michael Brown <mcb30@ipxe.org>