BACKPORT: xfrm: Add a new lookup key to match xfrm interfaces.

This patch adds the xfrm interface id as a lookup key
for xfrm states and policies. With this we can assign
states and policies to virtual xfrm interfaces.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Shannon Nelson <shannon.nelson@oracle.com>
Acked-by: Benedict Wong <benedictwong@google.com>
Tested-by: Benedict Wong <benedictwong@google.com>
Tested-by: Antony Antony <antony@phenome.org>
Reviewed-by: Eyal Birger <eyal.birger@gmail.com>

Conflicts: XFRM device offload not backported previously; reverted
codepaths that required device offload

(cherry picked from commit 7e6526404adedf079279aa7aa11722deaca8fe2e)
Signed-off-by: Benedict Wong <benedictwong@google.com>
Bug: 115914689
Change-Id: I45b6e316687599777a459ad1baea516afa8f473d