add bsn_time extension

This extension allows the controller to get a timestamp from the switch. This
will differ from the controller's time due to network latency, TCP queueing,
and queuing in the switch software.
diff --git a/openflow_input/bsn_time b/openflow_input/bsn_time
new file mode 100644
index 0000000..0a955be
--- /dev/null
+++ b/openflow_input/bsn_time
@@ -0,0 +1,54 @@
+// Copyright 2013, Big Switch Networks, Inc.
+//
+// LoxiGen is licensed under the Eclipse Public License, version 1.0 (EPL), with
+// the following special exception:
+//
+// LOXI Exception
+//
+// As a special exception to the terms of the EPL, you may distribute libraries
+// generated by LoxiGen (LoxiGen Libraries) under the terms of your choice, provided
+// that copyright and licensing notices generated by LoxiGen are not altered or removed
+// from the LoxiGen Libraries and the notice provided below is (i) included in
+// the LoxiGen Libraries, if distributed in source code form and (ii) included in any
+// documentation for the LoxiGen Libraries, if distributed in binary form.
+//
+// Notice: "Copyright 2013, Big Switch Networks, Inc. This library was generated by the LoxiGen Compiler."
+//
+// You may not use this file except in compliance with the EPL or LOXI Exception. You may obtain
+// a copy of the EPL at:
+//
+// http://www.eclipse.org/legal/epl-v10.html
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// EPL for the specific language governing permissions and limitations
+// under the EPL.
+
+// Request a timestamp during message processing.
+//
+// The timestamp is relative to when the switch sent the initial HELLO.
+// The intended use is in conjunction with barriers to approximately determine
+// time elapsed between processing two messages (such as stats requests).
+// The timestamp must be monotonic (not affected by system time updates).
+
+#version 4
+
+struct of_bsn_time_request : of_bsn_header {
+    uint8_t version;
+    uint8_t type == 4;
+    uint16_t length;
+    uint32_t xid;
+    uint32_t experimenter == 0x5c16c7;
+    uint32_t subtype == 44;
+};
+
+struct of_bsn_time_reply : of_bsn_header {
+    uint8_t version;
+    uint8_t type == 4;
+    uint16_t length;
+    uint32_t xid;
+    uint32_t experimenter == 0x5c16c7;
+    uint32_t subtype == 45;
+    uint64_t time_ms; /* Milliseconds since HELLO */
+};