ofproto-dpif: Fix GCC warning.

gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48) warned:

    ofproto/ofproto-dpif.c: In function 'bundle_send_learning_packets':
    ofproto/ofproto-dpif.c:1835: warning: dereferencing type-punned pointer
    will break strict-aliasing rules

I agree that its analysis matches what the C standard says.  This commit
fixes the problem and avoids the warning.

The assignment to 'port' isn't actually necessary.  I included it because
I like to have a variable with the correct type near the use of that type
through a "void *".  Then "grep" for that type is more effective, and the
compiler will be able to diagnose any later change to (in this case) the
type of the first parameter to send_packet().

Signed-off-by: Ben Pfaff <blp@nicira.com>

Author: blp

ofproto/ofproto-dpif.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009, 2010, 2011 Nicira Networks.
+ * Copyright (c) 2009, 2010, 2011, 2012 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -1816,11 +1816,15 @@ bundle_send_learning_packets(struct ofbundle *bundle)
         if (e->port.p != bundle) {
             struct ofpbuf *learning_packet;
             struct ofport_dpif *port;
+            void *port_void;
             int ret;
 
-            learning_packet = bond_compose_learning_packet(bundle->bond, e->mac,
-                                                           e->vlan,
-                                                           (void **)&port);
+            /* The assignment to "port" is unnecessary but makes "grep"ing for
+             * struct ofport_dpif more effective. */
+            learning_packet = bond_compose_learning_packet(bundle->bond,
+                                                           e->mac, e->vlan,
+                                                           &port_void);
+            port = port_void;
             ret = send_packet(port, learning_packet);
             ofpbuf_delete(learning_packet);
             if (ret) {