mlxsw: spectrum_router: Take router lock from inside routing code

There are several work items in the routing code that currently rely on
RTNL lock to guard against concurrent changes. Have these work items
acquire the router lock in preparation for the removal for RTNL lock
from the routing code.

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