GTPv2: Fix match of 15-digit IMSIs

15-digit IMSIs are len(imsi)=15, but decoded messages are
octet-aligned, hence the hexstring in messages is len(imsi)=16,
where the last hex char is a padding 'F'H.

* Make sure IMSIs stored in GTPv2_Emulation are padded to 16 digits (8
  octets) to process matches easily.
* Update tr_ template to transparently adapt passed hexstrings to match
  the octet-aligned value received from the wire.

Change-Id: Ie2f316ccb5bc69ec15e861616de4fd5babc4004e
3 files changed