Add dump() for WifiHealthMonitor

Add dump() for WifiHealthMonitor to help debugging with dumpsys or
bugreport.

Bug: 155245407
Test: manual test with "adb shell dumpsys wifi | grep WifiHealthMonitor
-c 15" to confirm message are printed properly.

Change-Id: I4ce71494f93114b869c22cf9559d9e6329a0a82d
4 files changed