controller: Add parameter for maximum log level to initiate/terminate_*()

controller: Add parameter for maximum log level to initiate/terminate_*()

Previously, the logger installed by the controller always announced
LEVEL_PRIVATE(4), which produced completely useless logging calls with
the common clients (vici/stroke) whose default log level is LEVEL_CTRL(1).
This can produce quite some overhead if there are e.g. a lot of concurrent
initiate() calls.