add vlr_subscr_find_by_mi

Will be used by I6fa37d6ca9fcb1637742b40e37b68d67664c9b60
"implement CM Re-Establish for voice calls"

Related: SYS#5130
Change-Id: I5291d098a02268bd1c2e30195ae61e4a13e8709c
2 files changed