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/ripngd/ripngd.c b/ripngd/ripngd.c
index dd54440..9105831 100644
--- a/ripngd/ripngd.c
+++ b/ripngd/ripngd.c
@@ -615,7 +615,7 @@
   struct access_list *alist;
   struct prefix_list *plist;
   int distribute = ripng_distribute == RIPNG_FILTER_OUT ?
-      DISTRIBUTE_OUT : DISTRIBUTE_IN;
+      DISTRIBUTE_V6_OUT : DISTRIBUTE_V6_IN;
   const char *inout = ripng_distribute == RIPNG_FILTER_OUT ? "out" : "in";
 
   /* Input distribute-list filtering. */
@@ -2757,9 +2757,9 @@
 
   ri = ifp->info;
 
-  if (dist->list[DISTRIBUTE_IN])
+  if (dist->list[DISTRIBUTE_V6_IN])
     {
-      alist = access_list_lookup (AFI_IP6, dist->list[DISTRIBUTE_IN]);
+      alist = access_list_lookup (AFI_IP6, dist->list[DISTRIBUTE_V6_IN]);
       if (alist)
 	ri->list[RIPNG_FILTER_IN] = alist;
       else
@@ -2768,9 +2768,9 @@
   else
     ri->list[RIPNG_FILTER_IN] = NULL;
 
-  if (dist->list[DISTRIBUTE_OUT])
+  if (dist->list[DISTRIBUTE_V6_OUT])
     {
-      alist = access_list_lookup (AFI_IP6, dist->list[DISTRIBUTE_OUT]);
+      alist = access_list_lookup (AFI_IP6, dist->list[DISTRIBUTE_V6_OUT]);
       if (alist)
 	ri->list[RIPNG_FILTER_OUT] = alist;
       else
@@ -2779,9 +2779,9 @@
   else
     ri->list[RIPNG_FILTER_OUT] = NULL;
 
-  if (dist->prefix[DISTRIBUTE_IN])
+  if (dist->prefix[DISTRIBUTE_V6_IN])
     {
-      plist = prefix_list_lookup (AFI_IP6, dist->prefix[DISTRIBUTE_IN]);
+      plist = prefix_list_lookup (AFI_IP6, dist->prefix[DISTRIBUTE_V6_IN]);
       if (plist)
 	ri->prefix[RIPNG_FILTER_IN] = plist;
       else
@@ -2790,9 +2790,9 @@
   else
     ri->prefix[RIPNG_FILTER_IN] = NULL;
 
-  if (dist->prefix[DISTRIBUTE_OUT])
+  if (dist->prefix[DISTRIBUTE_V6_OUT])
     {
-      plist = prefix_list_lookup (AFI_IP6, dist->prefix[DISTRIBUTE_OUT]);
+      plist = prefix_list_lookup (AFI_IP6, dist->prefix[DISTRIBUTE_V6_OUT]);
       if (plist)
 	ri->prefix[RIPNG_FILTER_OUT] = plist;
       else