smbd: Implement fsctl_set_reparse_point

smbd: Implement fsctl_set_reparse_point

Store the data in the "user.SmbReparse" xattr. Only allow this on
regular files. Windows does it for directories too, but we can not
allow this: Setting a symlink reparse point in a xattr on a directory
would go unnoticed by our openat2-optimization. If someone really
needs this, we could have a VFS module disallowing openat2 and doing
the appropriate checks on every openat-call.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>