Adds the control message handler to synchronize offloaded group config
with that of the kernel. Such messages are sent from fw to driver and
feature the following 3 flags:

- Data: an attached cmsg could not be processed - store for retransmission
- Xon: FW can accept new messages - retransmit any stored cmsgs
- Sync: full sync requested so retransmit all kernel LAG group info
Signed-off-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>