Support dissecting the TLV data format specified for Lwm2m

Support dissecting the TLV data format specified for Lwm2m

Lightweight M2M is a protocol on top of CoAP that is used for
device management. The specification contains a custom payload
format - a simple type, length, value binary encoding.

This patch adds support for dissecting this payload format.
While not yet officially registered, the main open source
implementation of the lwm2m protocol - eclipse's leshan - uses this
content type 1542 for its messages.

Bug: 12110
Change-Id: Ib022d1f485c706f1d69ceec7200790448d080965
Reviewed-on: https://code.wireshark.org/review/13835
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>