smbd: Hide the SMB1 posix symlink behaviour behind UCF_LCOMP_LNK_OK

smbd: Hide the SMB1 posix symlink behaviour behind UCF_LCOMP_LNK_OK

This will be used in the future to also open symlinks as reparse
points, so this won't be specific to only SMB1 posix extensions.

I have tried to avoid additional flags for several weeks by making
openat_pathref_fsp or other flavors of this to always open fsp's with
symlink O_PATH opens, because I think NT_STATUS_OBJECT_NAME_NOT_FOUND
with a valid stat is a really bad and racy way to express that we just
hit a symlink, but I miserably failed. Adding additional flags (another one
will follow) is wrong, but I don't see another way right now.

Signed-off-by: Volker Lendecke <vl@samba.org>