Add port attribute to get the max debug data size. (#2033)

Create a new port attribute to get the max size of the port debug data.
This can be read by the NOS to determine the size of the buffer to
allocate before reading the port debug data.

Signed-off-by: Mike Beresford <mberes@google.com>

Author: mikeberesford

inc/saiport.h

@@ -2520,6 +2520,14 @@ typedef enum _sai_port_attr_t
      */
     SAI_PORT_ATTR_POE_PORT_ID,
 
+    /**
+     * @brief The maximum size of SAI_PORT_ATTR_JSON_FORMATTED_DEBUG_DATA in bytes.
+     *
+     * @type sai_uint32_t
+     * @flags READ_ONLY
+     */
+    SAI_PORT_ATTR_JSON_FORMATTED_DEBUG_DATA_SIZE,
+
     /**
      * @brief End of attributes
      */