Wifi: Add some interface annotations

This commit adds some Wifi related interface annotations.
This includes:
    Annotations.WifiStandard
    Annotations.ChannelWidth
The commit also converts some APIs to @hide

Bug: 149420144
Test: Builds correctly (no new functionality in commit)
Change-Id: I007a7d828197e24e32d8f9bb558500e56d8b74dc