ixgbevf: add ixgbevf_rx_skb

This patch adds ixgbevf_rx_skb in line with how ixgbe handles the variations on
how packets can be received. It will be extended in a following patch for
CONFIG_NET_RX_BUSY_POLL support.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>