net: marvell: prestera: handle fib notifications

For now we support only TRAP or DROP, so we can offload only "local" or
"blackhole" routes.
Nexthop routes is TRAP for now. Will be implemented soon.

Co-developed-by: Taras Chornyi <tchornyi@marvell.com>
Signed-off-by: Taras Chornyi <tchornyi@marvell.com>
Co-developed-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu>
Signed-off-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu>
Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>