xfrm: Refuse to insert 32 bit userspace socket policies on 64 bit systems

We don't have a compat layer for xfrm, so userspace and kernel
structures have different sizes in this case. This results in
a broken configuration, so refuse to configure socket policies
when trying to insert from 32 bit userspace as we do it already
with policies inserted via netlink.

Reported-and-tested-by:  <syzbot+e1a1577ca8bcb47b769a@syzkaller.appspotmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>