Phone: Ignore restart ringer once silent requested when incoming call

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.

Change-Id: I7261a9b39c7d0965c96971fda7031b385c7a084f
Author: Zhuangzhi Li <zhuangzhi.li@intel.com>
Signed-off-by: Xiaokang Qin <xiaokang.qin@intel.com>
Signed-off-by: Beare, Bruce J <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 32156