mlxsw: spectrum_router: Add support for double entry RIFs

[ Upstream commit 5ca1b208 ]

In Spectrum-1, loopback router interfaces (RIFs) used for IP-in-IP
encapsulation with an IPv6 underlay require two RIF entries and the RIF
index must be even.

Prepare for this change by extending the RIF parameters structure with a
'double_entry' field that indicates if the RIF being created requires
two RIF entries or not. Only set it for RIFs representing ip6gre tunnels
in Spectrum-1.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 12ae97c5 ("mlxsw: spectrum_ipip: Fix memory leak when changing remote IPv6 address")
Signed-off-by: Sasha Levin <sashal@kernel.org>