rnd: break out prng from xutils

We only need it in curvetun, this makes it easier to maintain.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
xio: refactor fopencookie related functions

Again, we move them out of xio to shrink it down.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>