Fix variable-length managment packet dissection

Before, several managment packets were dissected incorrectly as
EPHandleDeleteReq's. Now they are dissected with the generic managment
packet dissector.

Change-Id: Id2f0951b91b99ba2340ff77c6285f382436788ef
Reviewed-on: https://code.wireshark.org/review/3328
Reviewed-by: Evan Huus <eapache@gmail.com>