wifi: Remove "Wlan" prefix from wifi_legacy_hal public methods

All the legacy HAL API's in the function table uses the "wlan0"
interface handle for the various operations. But, this is an internal
detail that should be abstracted inside WifiLegacyHal class. So, rename
the public methods to remove the "Wlan" prefix from them.

Also, add methods to fetch the iface names to use for the various types
of HAL.

Bug: 31943042
Test: Compiles
Change-Id: I35a6cdea0ad7cff295d33c0245953258129fba43