mlxsw: spectrum_router: Store NVE decapsulation configuration in router

When a host route is added, the driver checks if the route needs to be
promoted to perform NVE decapsulation based on the current NVE
configuration. If so, the index of the decapsulation entry is retrieved
and associated with the route.

Currently, this information is stored in the NVE module which the router
module consults. Since the information is protected under RTNL and since
route insertion happens with RTNL held, there is no problem to retrieve
the information from the NVE module.

However, this is going to change and route insertion will no longer
happen under RTNL. Instead, a dedicated lock will be introduced for the
router module.

Therefore, store this information in the router module and change the
router module to consult this copy.

The validity of the information is set / cleared whenever an NVE tunnel
is initialized / de-initialized. When this happens the NVE module calls
into the router module to promote / demote the relevant host route.

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