*
* This function checks that the message has a valid length for its particular
* type of message, and returns an error if not.
*
* In addition to setting '*typep', this function pulls off the OpenFlow header
* (including the stats headers, vendor header, and any subtype header) with
*
* This function checks that the message has a valid length for its particular
* type of message, and returns an error if not.
*
* In addition to setting '*typep', this function pulls off the OpenFlow header
* (including the stats headers, vendor header, and any subtype header) with