The current implementation of mxs_log_message() is otherwise
generic, but for the fact that the session id is automatically
injected into the message.
With this change, a mxs_log_init2() is introduced that in addition
to the existing parameters takes a function using which the context
can be provided. The implementation of mxs_log_init() now simply
calls mxs_log_init2() giving a function that provides the MaxScale
context.
This is in preparation for moving maxscale/log_manager.h to
maxbase/log.h.
f98cb0fe8d