The stream engine memory handling needed updating as it didn't scale. Changes:
- pools can now be initialized to size 0, meaning unlimited
- stream engine uses a memcap setting. Sessions, segments and aldata is part
of this, app layer state isn't.
- memory is accounted using a global int that is spinlocked.
- a counter for sessions that have not been picked up because of memcap was
added.
- all reassembly errors are converted to debug msgs.
- improve locking of application layer handling, making sure that the flow cannot be freed/cleared when the detection engine is still working with it.
- add a check to the app layer detection to make sure that a match function will only inspect an app layer state if it's of the right type.
Sets a flowbit with the sig id if the packet matches match. Checks
on that if the app layer matches match. Currently misuses the
flowbits api for this in a way that needs fixing.