packet-rsl: Fix dissection of "CB Command Type" IE

packet-rsl: Fix dissection of "CB Command Type" IE

The "CB Command Type" IE is described in 3GPP TS 48.058 Section 9.3.41,
and consists of three fields.  Prior to this patch, the dissector would
decode none of them and instead produce a non-applicable "channel type"
dissection.

Change-Id: Ibb97432871df1276524fe96512ac1b67d5c5d3f0
Reviewed-on: https://code.wireshark.org/review/29683
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>