net: dsa: qca8k: add support for mib autocast in Ethernet packet

The switch can autocast MIB counter using Ethernet packet.
Add support for this and provide a handler for the tagger.
The switch will send packet with MIB counter for each port, the switch
will use completion API to wait for the correct packet to be received
and will complete the task only when each packet is received.
Although the handler will drop all the other packet, we still have to
consume each MIB packet to complete the request. This is done to prevent
mixed data with concurrent ethtool request.

connect_tag_protocol() is used to add the handler to the tag_qca tagger,
master_state_change() use the MIB lock to make sure no MIB Ethernet is
in progress.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>