winbind: improve wb_domain_request_send() to use wb_dsgetdcname_send() for a foreign...

winbind: improve wb_domain_request_send() to use wb_dsgetdcname_send() for a foreign domain

Commit ed3bc614cccec6167c64ac58d78344b6426cd019 got the logic wrong while
trying to implement the logic we had in init_child_connection(),
which was removed by commit d61f3626b79e0523beadff355453145aa7b0195c.

Instead of doing a WINBINDD_GETDCNAME request (which would caused an error
because the implementation was removed in commit
958fdaf5c3ba17969a5110e6b2b08babb9096d7e), we sent the callers request
and interpreted the result as WINBINDD_GETDCNAME response, which
led to an empty dcname variable. As result the domain child
opened a connection to the primary domain in order to lookup
a dc.

If we want to connect the primary domain from the parent via
a domain child of the primary domain.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13295

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>