rocker: use FIB notifications instead of switchdev calls

Until now, in order to offload a FIB entry to HW we use switchdev op.
Use the newly introduced FIB notifier infrasturucture to process
FIB entries to offload the in HW.
Abort mechanism is now handled within the rocker driver.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>