This change makes it so that if UDP CSUM is not specified we will default
to enabling it.  The main motivation behind this is the fact that with the
use of outer checksum we can greatly improve the performance for GENEVE
tunnels on hardware that doesn't know how to parse them.
Signed-off-by: NAlexander Duyck <aduyck@mirantis.com>
Acked-by: NTom Herbert <tom@herbertland.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>