Revert "xfrm: rename xfrm_state_offload struct to allow reuse"

This reverts commit 837f37f0 which is
commit 87e0a94e upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ic73db3a65a2cf962225a77c16a2a6ecdd5ef9cb1
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>