e1000 (and e1000e, igb, ixgbe, ixgb) all do a series of
operations each time a multicast address is added.  The flow goes
something like

1) stack adds one multicast address
2) stack passes whole current list of unicast and multicast
   addresses to driver
3) driver clears entire list in hardware
4) driver programs each multicast address using iomem in a loop

This was causing multicast packets to be lost during the
reprogramming process.

reference with test program:
http://kerneltrap.org/mailarchive/linux-netdev/2009/3/14/5160514/thread

Thanks to Dave Boutcher for his report and test program.

This driver fix prepares an array all at once in memory and
programs it in one shot to the hardware, not requiring an "erase"
cycle.
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>