net/pcap: generate unique MAC addresses for interfaces

net/pcap: generate unique MAC addresses for interfaces

The MAC addresses are generated in a similar manner as in the TAP PMD,
where the address is based on the number of PCAP ports created.

This is useful for the purposes of debugging DPDK applications using
PCAP devices instead of real devices where multiple devices should still
have unique MAC addresses. This method was chosen over randomly
assigning MAC addresses to make the creation of pcaps, specifically
matching the destination ethernet address field to an interface, easier.

Signed-off-by: Cian Ferriter <cian.ferriter@intel.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>