bridge: mrp: Extend MRP netlink interface for configuring MRP interconnect

This patch extends the existing MRP netlink interface with the following
attributes: IFLA_BRIDGE_MRP_IN_ROLE, IFLA_BRIDGE_MRP_IN_STATE and
IFLA_BRIDGE_MRP_START_IN_TEST. These attributes are similar with their
ring attributes but they apply to the interconnect port.

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>