mlxsw: spectrum_router: Link CRIFs to RIFs

mlxsw: spectrum_router: Link CRIFs to RIFs

When a RIF is about to be created, the registration of the netdevice that
it should be associated with must have been seen in the past, and a CRIF
created. Therefore make this a hard requirement by looking up the CRIF
during RIF creation, and complaining loudly when there isn't one.

This then allows to keep a link between a RIF and its corresponding
CRIF (and back, as the relationship is one-to-at-most-one), which do.

The CRIF will later be useful as the objects tracked there will be
offloaded lazily as a result of RIF creation.

CRIFs are created when an "interesting" netdevice is registered, and
destroyed after such device is unregistered. CRIFs are supposed to already
exist when a RIF creation request arises, and exist at least as long as
that RIF exists. This makes for a simple invariant: it is always safe to
dereference CRIF pointer from "its" RIF.

To guarantee this, CRIFs cannot be removed immediately when the UNREGISTER
event is delivered. The reason is that if a RIF's netdevices has an IPv6
address, removal of this address is notified in an atomic block. To remove
the RIF, the IPv6 removal handler schedules a work item. It must be safe
for this work item to access the associated CRIF as well.

Thus when a netdevice that backs the CRIF is removed, if it still has a
RIF, do not actually free the CRIF, only toggle its can_destroy flag, which
this patch adds. Later on, mlxsw_sp_rif_destroy() collects the CRIF.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Link: https://lore.kernel.org/r/68c8e33afa6b8c03c431b435e1685ffdff752e63.1687438411.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>