Fix issue that DDS can not get back to primary sub and network mode shows incorrect in settings.

ModemBindingpPolicyHandler sends pref network mode to RIL, but even if
it fails, it also updates network mode to telephony DB.

Update the DB only on success of setting network mode for all subs.

CRs-Fixed: 789724

Change-Id: I1121d75226415d3b08c58a4aa1b6a3a060712511