Handle hiddenSSID as one of soft ap config for backup & restore

In addition to the change to persist hiddenSSID, this CL takes care of
backup and restore use case for hiddenSSID as one of soft ap config.

cherry-picked from aog/773385

Bug: 117052143
Test: Unit tests
Change-Id: I4af897f466c5d8fea66aec93e39faf3f13bd23fb
2 files changed