mlxsw: spectrum_router: Maintain a hash table of CRIFs

CRIFs are objects that mlxsw maintains for netdevices that may not have an
associated RIF (i.e. they may not have been instantiated in the ASIC), but
if indeed they do not, it is quite possible they will in the future. These
netdevices are candidate RIFs, hence CRIFs. Netdevices for which CRIFs are
created include e.g. bridges, LAGs, or front panel ports. The idea is that
next hops would be kept at CRIFs, not RIFs, and thus it would be easier to
offload and unoffload the entities that have been added before the RIF was
created.

In this patch, add the code for low-level CRIF maintenance: create and
destroy, and keep in a table keyed by the netdevice pointer for easy
recall.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Link: https://lore.kernel.org/r/186d44e399c475159da20689f2c540719f2d1ed0.1687438411.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>