net: geneve: accept every ethertype

The Geneve encapsulation, as defined in RFC 8926, has a Protocol Type
field, which states the Ethertype of the payload appearing after the
Geneve header.

Commit 435fe1c0c1f7 ("net: geneve: support IPv4/IPv6 as inner protocol")
introduced a new IFLA_GENEVE_INNER_PROTO_INHERIT flag that allowed the
use of other Ethertypes than Ethernet. However, it did not get rid of a
restriction that prohibits receiving payloads other than Ethernet,
instead the commit white-listed additional Ethertypes, IPv4 and IPv6.

This patch removes this restriction, making it possible to receive any
Ethertype as a payload, if the IFLA_GENEVE_INNER_PROTO_INHERIT flag is
set.

The restriction was set in place back in commit 0b5e8b8eeae4
("net: Add Geneve tunneling protocol driver"), which implemented a
protocol layer driver for Geneve to be used with Open vSwitch. The
relevant discussion about introducing the Ethertype white-list can be
found here:
https://lore.kernel.org/netdev/CAEP_g=_1q3ACX5NTHxLDnysL+dTMUVzdLpgw1apLKEdDSWPztw@mail.gmail.com/

<quote>
>> +       if (unlikely(geneveh->proto_type != htons(ETH_P_TEB)))
>
> Why? I thought the point of geneve carrying protocol field was to
> allow protocols other than Ethernet... is this temporary maybe?

Yes, it is temporary. Currently OVS only handles Ethernet packets but
this restriction can be lifted once we have a consumer that is capable
of handling other protocols.
</quote>

This white-list was then ported to a generic Geneve netdevice in commit
371bd1061d29 ("geneve: Consolidate Geneve functionality in single
module."). Preserving the Ethertype white-list at this point made sense,
as the Geneve device could send out only Ethernet payloads anyways.

However, now that the Geneve netdevice supports encapsulating other
payloads with IFLA_GENEVE_INNER_PROTO_INHERIT and we have a consumer
capable of other protocols, it seems appropriate to lift the restriction
and allow any Geneve payload to be received.

Signed-off-by: Josef Miegl <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Reviewed-by: Eyal Birger <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

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