[WifiCoex] Add shell commands for mocking cell channels

Add shell commands to set and reset mocked cell channels to pass through
the coex algorithm for testing purposes.

Bug: 153651001
Test: atest CoexManagerTest && atest WifiShellCommandTest
Change-Id: I201e9c0f61f8cdd6d9d918188220bb6c92d7f9b6
4 files changed