Changes

vlr: extend the subscriber invalidate callback with reasons

The VLR must be allowed to notify the MSC if a subscriber becomes invalid.
There are multiple cases when this happens:
a) if the subscriber didn't do a Location Update Procedure within the
given periodic timer.
b) if the HLR does a Cancel Location Procedure with reason withdraw
c) if the HLR does a Cancel Location Procedure with reason update location.
d) duplicate entries (unsure if this is valid, but keeping the code as is)

Change-Id: Ie5b687318b106a230fcee52deba86649641004b3

vlr: when receiving imsi detach, purge the subscriber towards HLR

The HLR must know when a subscriber has been disconnected.

Change-Id: I9c2569c45e69b422ce26050b682e6eb26c1c2625