Fix RAI construction

The gsm48_construct_ra() expect 6-byte buffer while ra_id.digits is
3-byte buffer. The function fills in LAC and RAC as well so we should
pass entire struct, not just 'digits' part which only store MCC/MNC.

Related: OS#1640
Change-Id: I3bfda930012c792452f9fd695ed7acf46365f1df
Fixes: CID57877, CID57876