BUG/MINOR: cli: fix CLI handler "set anon global-key" call

BUG/MINOR: cli: fix CLI handler "set anon global-key" call

Anonymization mode has two CLI handlers "set anon <on|off>" and "set
anon global-key". The last one only requires admin level. However, as
cli_find_kw() is implemented, only the first handler will be retrieved
as they both start with the same prefix "set anon".

This has the effect to execute the wrong handler for "set anon
global-key" with an error message about an invalid keyword. To fix this,
handlers definition have been separated for both "set anon on" and "set
anon off" commands. This allows to have minimal changes while keeping
the same "set anon" prefix for each commands.

Also take this opportunity to fix a reference to a non-existing "set
global-key" CLI handler in the documentation.

This must be backported up to 2.7.