wifi(interface): Add/Correct docstring params

Changes in the CL:
1. Add missing docstring params in the HIDL interface.
2. Reword some method docs. Occurences of "will" is replaced
by "must" (based on comments received on supplicant HIDL interface:
go/aog/275115).
3. Add onFailure callbacks for all the methods and added docstrings for
them.

Bug: 31352200
Test: mmma -j32 hardware/interfaces/wifi/1.0
Change-Id: Ib7152625851023d6244f742bb77a8fdc0829e00d