s3: smbd: Move the setting of the destructor of struct smb_Dir * up two levels.

s3: smbd: Move the setting of the destructor of struct smb_Dir * up two levels.

Previously, open_dir_safely() called OpenDir_internal() which
set the destructor.

Move setting the destructor into the callers of open_dir_safely()
as this will allow us to have different destructors for handle-based
calls.

The reason this is important is that I have a follow up patchset
that depends on this which makes all client directory enumerations
handle-based, calling OpenDir_fsp() only, and so the destructor there
will take care of the fsp back pointer.

Trying to keep a common destructor for handle-based and non-handle
based calls broke my brain when trying to separate the handle-based
calls from the non-handle based ones in my later patchset.

NB. The change in OpenDir_fsp() isn't a logic change as instead
of doing an early return from a function that sets the destructor,
we now fallthrough to setting the destructor then return, which
is identical.

Eventually the whole codepath using the fallback for non-handle
opens inside dptr_create() will go away and this simplifies the
code immensely. Some short term pain for long-term gain :-).

Added doxygen documentation as requested.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>