Fix potential NPE in WifiService dump

Added nullchecks to WifiServiceImpl & WifiMetrics dump methods usage of
args.
This is a precaution to similar null pointer exceptions that were occuring in
statemachine dump methods.

Bug: 37907061
Test: Added some unit tests
Change-Id: I0ab74421cddc31f7270cdd314fb86678194be0f0
4 files changed
tree: f698f9b02511de793641071506abf00fe351ed1b
  1. service/
  2. PREUPLOAD.cfg