mlxsw: spectrum_router: Take router lock from netdev listener

One entry point into the routing code is from the netdev listener block.
Some netdev events require access to internal router structures. For
example, changing the MTU of a netdev requires looking-up the backing
RIF and adjusting its MTU.

In order to serialize access to shared router structures, take the
router lock when processing netdev events that require access to it.

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