[WifiTrackerLib] Make WifiEntry scan result lists thread safe

The scan result lists of each WifiEntry is modified by the worker thread,
but clients on the main thread may need to iterate on the lists to
generate the verbose log. This may result in concurrent modification
exceptions, so we need to put locks on these lists.

Bug: 150978717
Test: build
Change-Id: Ice9f653b0496b20d87470ef0af1eda22a2d2fe9c
3 files changed