nfp: add support for multicast filter

Rewrite nfp_net_set_rx_mode() to implement interface to delivery
mc address and operations to firmware by using general mailbox
for filtering multicast packets.

The operations include add mc address and delete mc address.
And the limitation of mc addresses number is 1024 for each net
device.

User triggers adding mc address by using command below:
ip maddress add <mc address> dev <interface name>

User triggers deleting mc address by using command below:
ip maddress del <mc address> dev <interface name>

Signed-off-by: Diana Wang <na.wang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>