Format IPv6 policies correctly.

Previously we'd suppressed the mask-bits field in the output when
formatting a policy if it was >=32.  But that should be a >=128 if
we're talking about IPv6.

Since we didn't put these in descriptors, this bug affects only log
messages and controller outputs.

Fix for bug 16056.  The code in question was new in 0.2.0, but the
bug was introduced in 0.2.4 when we started supporting IPv6 exits.

changes/bug16056

@@ -0,0 +1,4 @@
+  o Minor bugfixes (relay, IPv6):
+    - When displaying an IPv6 exit policy, include the mask bits correctly
+      even when the number is greater than 31. Fixes bug 16056; bugfix on
+      0.2.4.7-alpha. Patch from "gturner".

src/or/policies.c

@@ -1391,9 +1391,9 @@ policy_write_item(char *buf, size_t buflen, addr_policy_t *policy,
   if (result < 0)
     return -1;
   written += strlen(buf);
-  /* If the maskbits is 32 we don't need to give it.  If the mask is 0,
-   * we already wrote "*". */
-  if (policy->maskbits < 32 && policy->maskbits > 0) {
+  /* If the maskbits is 32 (IPv4) or 128 (IPv6) we don't need to give it.  If
+     the mask is 0, we already wrote "*". */
+  if (policy->maskbits < (is_ip6?128:32) && policy->maskbits > 0) {
     if (tor_snprintf(buf+written, buflen-written, "/%d", policy->maskbits)<0)
       return -1;
     written += strlen(buf+written);