net: dcb: add CEE notify calls

net: dcb: add CEE notify calls

This adds code to trigger CEE events when an APP change or setall
command is made from user space. This simplifies user space code
significantly by creating a single interface to listen on that
works with both firmware and userland agents.

And if we end up with multiple agents this keeps every thing in
sync userland agents, firmware agents, and kernel notifier consumers.

For an example agent that listens for these events see:

https://github.com/jrfastab/cgdcbxd

cgdcbxd is a daemon used to monitor DCB netlink events and manage
the net_prio control group sub-system.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Shmulik Ravid <shmulikr@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>