bridge: mrp: Rework the MRP netlink interface

This patch reworks the MRP netlink interface. Before, each attribute
represented a binary structure which made it hard to be extended.
Therefore update the MRP netlink interface such that each existing
attribute to be a nested attribute which contains the fields of the
binary structures.
In this way the MRP netlink interface can be extended without breaking
the backwards compatibility. It is also using strict checking for
attributes under the MRP top attribute.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>