Changes

vlr: vlr_subscr_handle_cancel_req(): rework function

Invalid the subscriber towards the MSC/SGSN when receiving a Cancel Request from the HLR.
FIXME: canceling a fsm is still problematic if the VLR is in the middle of a LU, because it still
want to send back a failure when asked via HLR.

So when the HLR is doing a Cancel Location with reason Update Location (instead of withdrawn), the
VLR shouldn't allowed to transmit a Location Update Reject message..

Change-Id: Idf24d49cc6af53043da7ffaf7dda2993f2e812a5