dm: add 11-dm.rules for udev-168 and cleanup-db

add OPTIONS+="db_persist" to dm devices, to persist through a
udevadm info --cleanup-db

modules.d/90dm/11-dm.rules

@@ -0,0 +1,5 @@
+SUBSYSTEM!="block", GOTO="dm_end"
+KERNEL!="dm-[0-9]*", GOTO="dm_end"
+ACTION!="add|change", GOTO="dm_end"
+OPTIONS+="db_persist"
+LABEL="dm_end"

modules.d/90dm/module-setup.sh

@@ -25,5 +25,6 @@ install() {
     # Gentoo ebuild for LVM2 prior to 2.02.63-r1 doesn't install above rules
     # files, but provides the one below:
     inst_rules 64-device-mapper.rules
+    inst_rules "$moddir/11-dm.rules"
 }