replmd: Handle single-valued conflicts for an existing link

replmd: Handle single-valued conflicts for an existing link

Currently the code only handles the case where the received link
attribute is a new link (i.e. pdn == NULL). As well as this, we need to
handle the case where the conflicting link already exists, i.e. it's a
deleted link that has been re-added on another DC.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13055

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>