openflow_input: add BSN LACP stats request

This extension allows the controller to query LACP configuration and state from
the switch.
diff --git a/openflow_input/bsn b/openflow_input/bsn
index 0aa674b..dfbf981 100644
--- a/openflow_input/bsn
+++ b/openflow_input/bsn
@@ -46,3 +46,26 @@
     pad(4);
 };
 
+struct of_bsn_stats_request : of_experimenter_stats_request {
+    uint8_t version;
+    uint8_t type == 18;
+    uint16_t length;
+    uint32_t xid;
+    uint16_t stats_type == 0xffff;
+    enum ofp_stats_request_flags flags;
+    pad(4);
+    uint32_t experimenter == 0x5c16c7;
+    uint32_t subtype == ?;
+};
+
+struct of_bsn_stats_reply : of_experimenter_stats_reply {
+    uint8_t version;
+    uint8_t type == 19;
+    uint16_t length;
+    uint32_t xid;
+    uint16_t stats_type == 0xffff;
+    enum ofp_stats_reply_flags flags;
+    pad(4);
+    uint32_t experimenter == 0x5c16c7;
+    uint32_t subtype == ?;
+};