Use a custom init function for samba4 that sets a samba4

Use a custom init function for samba4 that sets a samba4
specific debug function.
By default do not debug, this is the most appropriate action for a library
as we cannot assume what stderr is use for in the main app.
The main app is responsible to set ev_debug_stderr if they so desire.
(This used to be commit e566a2f308ac6fb4b526a744f7059b565670aea5)