This adds support for the Trailer switch tagging format.  This is
another tagging that doesn't explicitly mark tagged packets with a
distinct ethertype, so that we need to add a similar hack in the
receive path as for the Original DSA tagging format.
Signed-off-by: NLennert Buytenhek <buytenh@marvell.com>
Tested-by: NByron Bradley <byron.bbradley@gmail.com>
Tested-by: NTim Ellis <tim.ellis@mac.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>