Revert "xfrm: rename xfrm_state_offload struct to allow reuse"

This reverts commit e4426baa 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: I6e16542895bf05cd0b1b29aabf262f07cfac4f88
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>