xfrm: store and rely on direction to construct offload flags

[ Upstream commit 482db2f1 ]

XFRM state doesn't need anything from flags except to understand
direction, so store it separately. For future patches, such change
will allow us to reuse xfrm_dev_offload for policy offload too, which
has three possible directions instead of two.

Reviewed-by: Raed Salem <raeds@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Stable-dep-of: 2cf567f4 ("netdevsim: copy addresses for both in and out paths")
Signed-off-by: Sasha Levin <sashal@kernel.org>