This command uses GetDiagnostics to show a list of connected
clients and some information about them. The information
contained for each connected station nearly maps 1:1 with the
station diagnostics information shown in "station <wlan> show"
apart from "ConnectedBss" which is now "Address".
Station, WSC, Ad-Hoc and AP family_arg_completion functions were
identical except for which commands they were referencing and the
interface type they were interested in. Combine all these into a single
function.
