WificondScanner: Use nanoseconds to reduce the round error

Use nanoseconds to log the scan start time to avoid the rounding error
that can happen when converting from micros to millis to filter stale
scan results.

Bug: 177888569
Test: atest com.android.server.wifi.scanner
Change-Id: I80ff3a1ee2b22039d0c186c352445aec932a2047
3 files changed