Pull up following revision(s) (requested by knakahara in ticket #304):
sys/net/if_loop.c: revision 1.95
loop_clone_create() must be called after ncpu is counted up for all CPUs.
loop_clone_create() uses ncpu in the following call-path.
    - loop_clone_create()
      - if_attach()
        - if_percpuq_create()
          - softint_establish() // use ncpu
          - percpu_foreach() // use ncpu
However, loopinit() of built-in module is called from
module_init_class(MODULE_CLASS_DRIVER) which is called before ncpu is counted
up in some architectures. So, It is too fast.
On the other hand, it is too late for rump netinet component to call
loop_clone_create() in config_finalize().
As the result, loop_clone_create() shuld be called in loopattach() for built-in
module, and in loopinit() for dynamic module.

(snj)