Merge branch 'xfrm: some fixes for GSO with SW crypto'

Sabrina Dubroca says:

====================
This series fixes a few issues with GSO. Some recent patches made the
incorrect assumption that GSO is only used by offload. The first two
patches in this series restore the old behavior.

The final patch is in the UDP GSO code, but fixes an issue with IPsec
that is currently masked by the lack of GSO for SW crypto. With GSO,
VXLAN over IPsec doesn't get checksummed.
====================

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>