wifi: Add SAP supported band feature flag

Settings can use band supported feature flag with API:
areFeaturesSupported to know what is the supported band on SoftAp.

Also: correct the java doc, use @code to indicate overlay configuration.

Bug: 168046702
Test: atest -c FrameworksWifiTests
Test: atest -c FrameworksWifiApiTests
Change-Id: Idbf8cb8bae3be613ebab0f7483c2f1ea954afccd
4 files changed