pfctl: optionally clarify which anchors are layer 3 and which are Ethernet

When listing anchors pfctl lists both 'regular' layer 3 anchors and
Ethernet anchors. It's possible to have the same anchor name in both,
which can be confusing.

Mitigate this a little by explicitly marking where the Ethernet anchors
start. Avoid breaking scripts by only doing this at the second level
of verbosity.

Sponsored by: Rubicon Communications, LLC ("Netgate")