CAPWAP: Use standard boilerplate (see doc/packet-PROTOABBREV.c)

For hf field, reindent code
Use 0x0 by default for bitmask
Remove also some "boilerplate" comment..

Change-Id: I552ccca2e444f3686ee9ecdad456f2ecfbaa5cba
Reviewed-on: https://code.wireshark.org/review/3953
Reviewed-by: Anders Broman <a.broman58@gmail.com>