bridge: mrp: Validate when setting the port role

This patch adds specific checks for primary(0x0) and secondary(0x1) when
setting the port role. For any other value the function
'br_mrp_set_port_role' will return -EINVAL.

Fixes: 20f6a05e

 ("bridge: mrp: Rework the MRP netlink interface")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>