mlxsw: spectrum_router: Add FIB abort warning

Add a warning that the abort mechanism was triggered for device.
Also avoid going through the procedure if abort was already done.

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