This is still an issue as of OpenBSD 5.6. Here is an updated patch for the latest 2.7 branch:

diff -r 88de50c1696b Modules/socketmodule.c
--- a/Modules/socketmodule.c    Sun Dec 28 18:51:25 2014 +0200
+++ b/Modules/socketmodule.c    Sun Dec 28 21:24:41 2014 -0500
@@ -1881,24 +1881,29 @@
 {
     int level;
     int optname;
     int res;
     char *buf;
     int buflen;
     int flag;
 
     if (PyArg_ParseTuple(args, "iii:setsockopt",
                          &level, &optname, &flag)) {
         buf = (char *) &flag;
         buflen = sizeof flag;
+        /* Multi cast options take shorter arguments */
+        if (optname == IP_MULTICAST_TTL
+            || optname == IP_MULTICAST_LOOP)
+                buflen = sizeof(u_char);
+         buf = (char *) &flag;
     }
     else {
         PyErr_Clear();
         if (!PyArg_ParseTuple(args, "iis#:setsockopt",
                               &level, &optname, &buf, &buflen))
             return NULL;
     }
     res = setsockopt(s->sock_fd, level, optname, (void *)buf, buflen);
     if (res < 0)
         return s->errorhandler();
     Py_INCREF(Py_None);
     return Py_None;