filter: HWHDR: re-order KEY_RAW_MAC checks

filter: HWHDR: re-order KEY_RAW_MAC checks

Currently, in `interp_mac2str` we have:

  if (/* KEY_RAW_MAC is valid */) {
    /*
     * set mac type
     */
  }

  if (/* mac type is ethernet */)
    // parse ethernet

  if (/* KEY_RAW_MAC is not valid */)
    // return early.

The MAC type will not be set to ethernet unless KEY_RAW_MAC is valid,
so we can move the last check up and drop the first one:

  if (/* KEY_RAW_MAC is not valid */)
    // return early.

  /*
   * set mac type
   */

  if (/* mac type is ethernet */)
    // parse ethernet

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>