Merge branch 'mlxsw-GRE-Offload-decap-without-encap'

Jiri Pirko says:

====================
mlxsw: GRE: Offload decap without encap

Petr says:

The current code doesn't offload GRE decapsulation unless there's a
corresponding encapsulation route as well. While not strictly incorrect (when
encap route is absent, the decap route traps traffic to CPU and the kernel
handles it), it's a missed optimization opportunity.

With this patchset, IPIP entries are created as soon as offloadable tunneling
netdevice is created. This then leads to offloading of decap route, if one
exists, or is added afterwards, even when no encap route is present.

In Linux, when there is a decap route, matching IP-in-IP packets are always
decapsulated. However, with IPv4 overlays in particular, whether the inner
packet is then forwarded depends on setting of net.ipv4.conf.*.rp_filter. When
RP filtering is turned on, inner packets aren't forwarded unless there's a
matching encap route. The mlxsw driver doesn't reflect this behavior in other
router interfaces, and thus it's not implemented for tunnel types either. A
better support for this will be subject of follow-up work.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>