SystemUI: reactivate WiFi activity indicators

One of the recent commits (MSIM) removed the wifi service listeners
in NetworkController.java. This commit adds it back again.

Change-Id: I03bea814fac82bfe76a51cde6c29f25887f56e12
Merge "SystemUI: reactivate WiFi activity indicators" into cm-11.0
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0