docs: xfrm: include mark in XFRM_MSG_MIGRATE_STATE EEXIST tuple
Document mark as part of the EEXIST tuple and update the SA lookup
description to match.
Fixes: c13c0cc6f52e ("xfrm: add documentation for XFRM_MSG_MIGRATE_STATE")
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>