lib: Make distribute.c accepts both v4 and v6.

distribute.c doesn't allow to manage both v4 and v6 distribute lists.  This
patch fix this problem by having 4 DISTRIBUTE* values in the enumeration instead
of two. The code in all daemons using distribute.c is adapted.
diff --git a/lib/distribute.h b/lib/distribute.h
index a2ffffd..e9625a3 100644
--- a/lib/distribute.h
+++ b/lib/distribute.h
@@ -29,8 +29,10 @@
 /* Disctirubte list types. */
 enum distribute_type
 {
-  DISTRIBUTE_IN,
-  DISTRIBUTE_OUT,
+  DISTRIBUTE_V4_IN,
+  DISTRIBUTE_V6_IN,
+  DISTRIBUTE_V4_OUT,
+  DISTRIBUTE_V6_OUT,
   DISTRIBUTE_MAX
 };