net: marvell: prestera: Refactor router functions

* Reverse xmas tree variables order
* User friendly messages on error paths
* Refactor __prestera_inetaddr_event to use early return

Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Link: https://lore.kernel.org/r/20220111011051.4941-1-yevhen.orlov@plvision.eu


Signed-off-by: Jakub Kicinski <kuba@kernel.org>