net/samba422: Fix location of ldb files

- Use SAMBA_LDB_MODULESDIR consistently
- Move all AD_DC-related plist entries to pkg-plist.ad_dc

This patch fixes a simple "make package" build with default options.

PR:		291541
Reported by:	O. Hartmann <ohartmann@walstatt.org>
Sponsored by:	Klara, Inc.