Adds pulling for network bytes for statsd.

Adds atoms to collect network bytes transmitted and received via wifi
and mobile data. We need to get the list of correct ifaces from
BatteryStats since NetworkStatsService only tracks the mobile ifaces.
We split the atoms so that we can also capture metrics sliced on
foreground and background since they are available from the kernel.
Also adds an atom for the Kernel Wakelocks.

Test: Manually tested with adb shell cmd stats pull-source after
modifying the StatsPullerManager.cpp

Change-Id: I9467afad799c6d97560e868f8625fefae5c2b5e1