PhoneWindowManager: allow volume keys in VoIP calls and screen off

Apply the same rule for volume keys during VoIP calls as during
PSTN calls allowing to change call volume when when the screen
is off.

Bug: 37571875
Test: Check volume keys work in Hangouts. Check regressions for music
and PSTN call volume

Change-Id: I2d5c654af47ade99ff4cb326e54e734087f5e8ae
1 file changed