i40evf: transmit and receive functionality

This file contains the transmit, receive, and NAPI functionality.

Some of the functions in this module are extracted from the i40e driver
but functions that are not appropriate for virtual function devices have
been removed.
Signed-off-by: NMitch Williams <mitch.a.williams@intel.com>
Signed-off-by: NGreg Rose <gregory.v.rose@intel.com>
Tested-by: NSibai Li <sibai.li@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>