datapath: geneve: Relax MTU constraints.

datapath: geneve: Relax MTU constraints.

Upstream commit:
    Allow the MTU of geneve devices to be set to large values, in order to
    exploit underlying networks with larger frame sizes.

    GENEVE does not have a fixed encapsulation overhead (an openvswitch
    rule can add variable length options), so there is no relevant maximum
    MTU to enforce.  A maximum of IP_MAX_MTU is used instead.
    Encapsulated packets that are too big for the underlying network will
    get dropped on the floor.

    Signed-off-by: David Wragg <david@weave.works>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Upstream: 55e5bfb53cff ("geneve: Relax MTU constraints")
Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Jesse Gross <jesse@kernel.org>