sfc: correctly support non-partial GSO_UDP_TUNNEL_CSUM on EF100

By asking the HW for the correct edits, we can make UDP tunnel TSO
 work without needing GSO_PARTIAL.  So don't specify it in our
 netdev->gso_partial_features.
However, retain GSO_PARTIAL support, as this will be used for other
 protocols later.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Martin Habets <mhabets@solarflare.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>