Changes

vlr: add PS support

Add vlr_ra_update() similar to vlr_lu_update().
Implement resending of GMM PDUs. While CS has a reliable connection
between the MS and MSC, the MS and SGSN doesn't have such connection.
The PDU is resend N times before the LU fsm is failing.

Change-Id: Ie9ffeb140c9d354b3a0f4822e2619f623235add0