ixgbe: fix multiple unicast address support

Multiple unicast address support appears to have been broken with the
change to support net_device_ops.  This a regression from 2.6.28 to 2.6.29.

I'm not 100% on whether ndo_set_multicast_list can be NULL after this
or not.  If ndo_set_rx_mode is set everything _should_ be using it.

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Acked-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>