Split ws80211_get_phys callback handler

Split up the ws80211_get_phys parser callback handler function into
separate functions for each attribute parsed. This is done in
preparation for supporting split wiphy dump feature where the function
logics will need modications.

Change-Id: Ic0b497fc628f0e7453cd62eb8199f17f9a308a7f
Reviewed-on: https://code.wireshark.org/review/4610
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Evan Huus <eapache@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>