Delay unmuting sensor when device is unlocked

The sensor privacy service also checks if the device is locked before
unmuting as an extra layer of security. It appears that the callback
when requesting unlock is invoked before the state in KeyguardManager is
updatd so we need to delay our call to unmute.

Test: Set pin and unblock camera
Fixes: 189946442
Change-Id: Ic9bf1a6abb9073acb11d9b569efcc665eacff63f