net: geneve: support IPv4/IPv6 as inner protocol

This patch adds support for encapsulating IPv4/IPv6 within GENEVE.

In order to use this, a new IFLA_GENEVE_INNER_PROTO_INHERIT flag needs
to be provided at device creation. This property cannot be changed for
the time being.

In case IP traffic is received on a non-tun device the drop count is
increased.

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Link: https://lore.kernel.org/r/20220316061557.431872-1-eyal.birger@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>