gbproxy: Implement TLLI cache and use it for SUSPEND/RESUME

When routing a SUSPEND/RESUME we need to keep track of where it came
from so we can send the (N)ACK back to the correct BSS. Use the TLLI
which is present in both messages to cache and retrieve the correct BSS.

A timer runs every two seconds and expires entries that are older than
the timeout (hardcoded to 5 seconds for now).

Related: SYS#4865, OS#4472
Change-Id: I42adf70f560d2bb358a9e1c7614281e8d2967568
3 files changed