dpif-netdev: Fix memory leak.

upcall->packet is allocated with malloc(), via ofpbuf_new(), but nothing
ever frees it.

Found by valgrind.

CC: Ed Maste <emaste@freebsd.org>
Signed-off-by: Ben Pfaff <blp@nicira.com>

lib/dpif-netdev.c

@@ -966,6 +966,7 @@ dpif_netdev_recv(struct dpif *dpif, struct dpif_upcall *upcall,
 
         ofpbuf_uninit(buf);
         *buf = *upcall->packet;
+        free(upcall->packet);
 
         return 0;
     } else {