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: Iede4972ab02e043091349777a5ac3109ec9e1fcb
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>