Phone: Ignore restart ringer once silent requested when incoming call

Credit: Zhuangzhi Li
Issue: When incall coming, press volume key can make the ringing silent, but
after you select SMS and cancel the dialog box, the ringer re-started.

Solution: Once silent requested when incoming call, keep ringer tone silent
until the call end.

Solution: Once silent requested when incoming call, keep ringer tone silent
until the call end.