Persist hiddenSSID for soft ap

hiddenSSID value is properly handled in underlying layer
incl. HostapdHal. However it's not persisted as one of
soft ap configuration.

cherry-picked from aog/773365

Bug: 117052143
Test: Manual
Test: Unit test
Change-Id: I11db9cd356ce3b1f3ce2e15e3b0bf71d85d8d40b
2 files changed