In order to prevent the issue where the xtra server url
that stored in gps.conf is incorrect (like xtra.bin instead
of xtra2.bin) for a particular modem, I've made this change
so that the xtra server url can be queried through loc api.
CRs-fixed: 366599
Change-Id: If65de98d837f068fd61a235cbf1104026246e5a9