vlr_access_req_fsm.c: use osmo_strlcpy and avoid compiler error

gcc 8.1.0:
../../../../src/osmo-msc/src/libvlr/vlr_access_req_fsm.c:679:3: error: ‘strncpy’ output may be truncated copying 15 bytes from a string of length 31 [-Werror=stringop-truncation]
   strncpy(par->imsi, mi_string, sizeof(par->imsi)-1);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Mobile Identity is a union of various kinds, but the IMSI is at most 15
digits, so truncation is "intended". I hope other layers validate the correct
length of an IMSI MI.

Change-Id: I0a17a188fc91e42e252ae4bf1d6cd0bf0e5eb077
1 file changed