packet-k12.c: Various minor changes:

- Simplify proto_reg_handoff() & move it to the end of the file as per convention;
- Reformat hf[] & ei[] for readability;
- Add editor modelines & do whitespace changes.

Change-Id: If01432c5b86129aaaab478493bbb218295bcb65c
Reviewed-on: https://code.wireshark.org/review/3622
Reviewed-by: Bill Meier <wmeier@newsguy.com>