Wi-SUN Protocol dissection and IEEE 802.15.4 IE cleanup.

Wi-SUN Protocol dissection and IEEE 802.15.4 IE cleanup.

This patch adds dissection for the Wi-SUN Field Area Network standard. Wi-SUN
packets are encoded as a collection of IEEE 802.15.4 information elements. This
required a bit of refactoring in how the IE dissector table is handled so that
external protocols could supply their own dissectors.

While I was working with the IEs, I also added support for the TSCH Timeslot and
Global Time IEs from the IEEE 802.15.4 standard in addition to some general
cleanup.

Change-Id: I2858e4ab577756568e33b86adfe282967899abd5
Reviewed-on: https://code.wireshark.org/review/24331
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>