xfrm: rely on XFRM offload

After change of initialization of x->type_offload pointer to be valid
only for offloaded SAs. There is no need to rely on both x->type_offload
and x->xso.type to determine if SA is offloaded or not.

Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>