gbproxy: Add VTY parameter: link stored-msgs-max-length

It was discovered in some prod setups that some TLLIs can maintain quite
long queues of msgb in case its IMSI is not acquired and the tlli is not
pruned due to link-list max-{age,length} being set to 0. As a result,
the osmo-gpbroxy steadly increases the list size of maintained TLLIs, and
some TLLI was found without IMSI catching already 1211 msgb.

Let's allow setting a maxiumum length for the queue storing those msgb
in a per TLLI base. If the limit is reached, oldest msgb are removed
before adding a new one.

Depends: libosmocore Change-Id I33b501e89a8f29e4aa121696bcbb13d4b83db40f

Related: SYS#4297

Change-Id: I4473be8604f80302df03ffdd5a13280dc072f824
3 files changed