nitb: Add subscriber delete command
mgcp: We only look at the RTP header use that in the comment
mgcp: Move Annex A counting out of patch/count method

mgcp_patch_and_count has grown due supporting linearizing timestamps,
ssrc and other things for equipment like the ip.access nanoBTS. Fight
back and move the Annex A code into a dedicated method.

The result is updated as we now count after all the patching and for
the Annex A code no change in SSRC can be detected.
mgcp: Do not detect the initial package as a wrap around

The Annex A code has a probation period but we don't have it. When
starting with seq_no==0 do not assume that the sequence numbers
have wrapped. Do it by moving the entire checking code into the
else.
mgcp: Count the incoming data instead of the modified one

For jitter, transit and packet loss we should count the data
that arrived and not the data we send towards the remote. This
is changing the jitter timings to what they were before the
re-factoring.

For forced timing we might willingly add jumps in the sequence
number but for jitter and packet loss we are more interested
in the data that traveled through the wire/air.
sgsn: Add boilerplate code for a SGSN test
sgsn: Create testcase that verifies that llmes get deleted

On an "unassignment" this code verifies that the LLME will vanish
from the list of LLMEs. We assume that this doesn't create a
memory leak.
sgsn: Add test that exposes a dangling pointer to the LLME

On detach the LLME get's unassigned (and hence destroyed) but the
GMM context will still point to that dead structure.
sgsn: Free MM context after receiving a Detach Request

On a Detach/Re-attach cycle the Address Sanitizer detected a
use-after-free kind of problem. That is because we tried to
destroy the LLME twice. The first time it is destroyed as part
of the Detach handling ans the second time it is destroyed as
part of destroying the old MM context.

In case the GPRS GMM detach message is lost the SGSN needs
to reply besides not having a MM entry.

The alternative would have been to add NULL checks for all
usages of ctx->llme which would not have helped with the
readability.

Sponsored-by: On-Waves ehf
sgsn: Add testcase for "re-transmission" of detach message

This currently shows that the LLME will remain allocated and
never be freed.