Pass loopback packets with source MAC matching device MAC

* Modified logic to pass incoming packets whose source MAC address
  matches the device's MAC address, incrementing the PASSED_LOOPBACK
  counter.
* Planned future change: Experimentally drop these packets instead of
  passing them.

Test: TH
Change-Id: I7910cb577c18de09c96ccee6823db469e90285b2
4 files changed