Proper calculation for overall WiFi MC statistics

In current implementations the WiFi MC statistcs are calculating by
aggregating the per uid statistics accross all UIDs. This does not
result in the correct values in case of time overlapping acquisitions of
MC wakelocks by same or different UIDs
This commit creates a separate Timer instance that tracks the actual
time spent with MC Enabled.

Bug: 69854369
Test: Manual Test

Change-Id: I78533f48300bc9faccc374d684698dae647bde5d
Signed-off-by: Ahmed ElArabawy <arabawy@google.com>