vxlan: Add new UDP encapsulation offload type for VXLAN-GPE

vxlan: Add new UDP encapsulation offload type for VXLAN-GPE

The fact is VXLAN with Generic Protocol Extensions cannot be supported by
the same hardware parsers that support VXLAN.  The protocol extensions
allow for things like a Next Protocol field which in turn allows for things
other than Ethernet to be passed over the tunnel.  Most existing parsers
will not know how to interpret this.

To resolve this I am giving VXLAN-GPE its own UDP encapsulation offload
type.  This way hardware that does support GPE can simply add this type to
the switch statement for VXLAN, and if they don't support it then this will
fix any issues where headers might be interpreted incorrectly.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>