net: lan966x: Expose lan966x_switchdev_nb and lan966x_switchdev_blocking_nb

Expose lan966x_switchdev_nb and lan966x_switchdev_blocking_nb to the
lan966x_main.h file because they will be needed by the lag driver.

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