PROTOABBREV: minor fix

Fix typo PROTO_ABBREV -> PROTOABBREV
Uncomment FIELDCONVERT

Change-Id: I7b64c09ecf0c22a38042156d958e1c6c850c839a
Reviewed-on: https://code.wireshark.org/review/3914
Reviewed-by: Anders Broman <a.broman58@gmail.com>