Make sure all saved networks have rand mac at bootup

When the device is updated to Q for the first time, generate
randomized MAC address and store them to permanent storage.

Bug: 122991465
Test: unit tests
Test: flash P build, add networks, then flash new build. Verify that the
randomized MAC address stays the same after forgetting and re-adding
those saved networks.

Change-Id: I6dadc0f730bdf49dd0d2ca094dd6b75d1abea69a
2 files changed