InCallUI: Speaker proximity only while in call (3/3)

Gives the option to only enable the speaker proximity
        feature during incall (speaker won't turn on
        while the phone is ringing, but will turn on
        after you remove the phone from your face, only
        after the receiving party has answered the call).

Change-Id: Ie1603f20ca306f0b08cf3f78b8593ac840a61179