bridge: uapi: mrp: Extend MRP attributes to get the status

Add MRP attribute IFLA_BRIDGE_MRP_INFO to allow the userspace to get the
current state of the MRP instances. This is a nested attribute that
contains other attributes like, ring id, index of primary and secondary
port, priority, ring state, ring role.

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>