Fix port throughput related statistics for i40e virtual functions

Fix port throughput related statistics for i40e virtual functions

When CRC stripping is enabled (default PROX behavior), the number of
rx bytes received by the NIC returned by DPDK usually does not take the
CRC 4 bytes into account.
However, for i40e virtual functions those 4 bytes are counted as part of
the received bytes. This resulted in both DPDK and PROX taking those 4 bytes
into account causing the RX % to be above 100%.

Change-Id: I59883b638ed67a6778f80c4dd6bfbfc4f9f2f528
Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>