s390/qeth: drop qeth_l2_del_all_macs() parameter

The only caller passes del = 0, so remove both the parameter and
the code that handles != 0.

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