Add support for counting non dataplane related packets

Add support for counting non dataplane related packets

When performing some zero packet loss performance testing on dataplane, it
is important (not) to count non dataplane packets. For instance, one might
receive uexpected packets from a switch, or ARP packets. Or one might need
to transmit ARP packets. Such packets should not be counted as dataplane
packets as for thse packets there is no 1:1 mapping between transmitted
packets and received packets.
To support this, the counters reporting numbers of transmitted and received
packets remain unchanged but two new counters have been added to PROX,
counting respectively number of received and number of transmitted
non-dataplane packets.
On RX side, packets are counsidered as non-dataplane if being ARP or if
they do not countain the proper signature
On TX side, ARP packets are not considered as dataplane packets.
This feature requires configuration of signature.
"dp core stats" command has been added

Change-Id: I98e113cd02f36d540383d343a433592867ad86a9
Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>