openflow_input: fix of_instruction_goto_table definition

The OF 1.4.0 spec says it has a table_id and padding just like in OF 1.3. I'm
not sure where the exp_data came from.
diff --git a/openflow_input/standard-1.4 b/openflow_input/standard-1.4
index 5766411..ea1c6fe 100644
--- a/openflow_input/standard-1.4
+++ b/openflow_input/standard-1.4
@@ -978,7 +978,8 @@
 struct of_instruction_goto_table : of_instruction {
     uint16_t type == 1;
     uint16_t len;
-    of_octets_t exp_data;
+    uint8_t table_id;
+    pad(3);
 };
 
 struct of_instruction_write_metadata : of_instruction {