Bluetooth: A2DP: APT-X does not use RTP while there is no content protection

Change-Id: I5ff8ffdda827b08ee7e284c15e70dadc368b009e
Reviewed-on: https://code.wireshark.org/review/4906
Petri-Dish: Michal Labedzki <michal.labedzki@tieto.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michal Labedzki <michal.labedzki@tieto.com>