GTP: allow empty Data Record Packet IE

Bug: 10277
Change-Id: I4edf330fa1c44a52d985d70555c7756954fb9364
Reviewed-on: https://code.wireshark.org/review/3008
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
(cherry picked from commit 826bca091874e04ce5aa72fa233df652bf8819fb)
Reviewed-on: https://code.wireshark.org/review/3009