Logcat: Add support for conversion from Exported PDU

Exported PDU may contains (Binary) Logcat, so it is possible to
"export" logcat binary from it.

Change-Id: Ic6607126e739ea3972b46c2bf19f064597d4e970
Reviewed-on: https://code.wireshark.org/review/3001
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>
Tested-by: Michal Labedzki <michal.labedzki@tieto.com>