Gracefully handle a case where success and expire could fire... I'm
only hitting this when doing something evil to simulate network code
but it seems appropriate to handle this gracefully.
tmsi is four octets long, there is no need to make it a string
and then jump through hoops to convert it to a number. Keep the database
using it as a string to benefit from the NULL handling of the db.
Introduce the reserved tmsi which has all bits set to 1 according
to GSM 03.03 §2.4 and start checking for it and make sure the db
code will never allocate such a tmsi.
For the BSC part we still assign a gsm_subscriber to lchan but it
might only contain the TMSI of this subscriber.
For the MSC part we will need the HLR/VLR feature of the gsm_subscriber,
specially the lookup's by number...
So if libbsc.a/libmsc.a are compiled in one app and used the
subscribers will be shared, and if only libbsc.a gets used we will
have more empty gsm_subscriber.c..