s390/qeth: Remove unused code

1. options.add_hhlen is set but never used, drop it
2. clean up no longer required forward declarations
3. delete all sorts of unused defines

Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Reviewed-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>