Revert "xfrm: For 32/64 compatability wrt. xfrm_usersa_info"

This reverts commit fc8c7dc1.

As indicated by Jiri Klimes, this won't work.  These numbers are
not only used the size validation, they are also used to locate
attributes sitting after the message.

Signed-off-by: David S. Miller <davem@davemloft.net>