Effects: set effect monitor flag to track volume

use effect volume monitor flag to get requested volume from
audio framework.

Bug: 123251705
Test: on/off equalizer on spotify/google music
      switch songs with equalize

Change-Id: I0db8019a00b08fcbec096ff7d6581c26d35ee752
Signed-off-by: Jasmine Cha <chajasmine@google.com>