If a MS changes RA, the RA will arrive in the new cell using the old
TLLI (masked as foreign TLLI). So we need to look-up the TLLI
in a special way, using the old RA as indicated in the 04.08 GMM
message.
There is still another bug remaining: As we somehow create a new LLC,
the sequence numbers of our responses start from 0 again, which is not
what the MS expects. This needs to be fixed in a follow-up patch.