net/mlx4_en: Re-design multicast attachments flow

Currently, for every change in the net device multicast list, the driver
detaches all the addresses from the HW device, and then attaches the
updated list. This behavior is wrong from two aspects: first, it causes
a load of firmware commands and second, there is period of time where
the correct addresses are not attached, which turned into packet loss.

To improve - a copy of the multicast list is saved by the driver. For
every change in the multicast list, the multicast list copy is used
to find the delta between those two lists and add or remove multicast
addresses as needed.

Reported-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Cc: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Hadar Hen Zion <hadarh@mellanox.co.il>
Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>