i40evf: refactor receive routine

i40evf: refactor receive routine

Orabug: 23176970

This is part 2 of the Rx refactor series, just including
changes to i40evf.

This refactor aligns the receive routine with the one in
ixgbe which was highly optimized.  This reduces the code
we have to maintain and allows for (hopefully) more readable
and maintainable RX hot path.

In order to do this:
- consolidate the receive path into a single function that doesn't
  use packet split but *does* use pages for Rx buffers.
- remove the old _1buf routine
- consolidate several routines into helper functions
- remove VF ethtool control over packet split
- remove priv_flags interface since it is unused

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit ab9ad98eb5f95b86490cc4c2ddbde5a0bc9bd5c6)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	drivers/net/ethernet/intel/i40evf/i40e_txrx.c