Revert "Fix bug allowing the comparison of v4 and v6 prefixes."

That patch was fixing a little bug, but makes another bigger one.
The previous patch fixes both.

This reverts commit e687a58f.

util.c

@@ -496,9 +496,6 @@ prefix_cmp(const unsigned char *p1, unsigned char plen1,
 {
     int plen = MIN(plen1, plen2);
 
-    if(v4mapped(p1) != v4mapped(p2))
-        return PST_DISJOINT;
-
     if(memcmp(p1, p2, plen / 8) != 0)
         return PST_DISJOINT;