scope cleanup. with this change

scope cleanup.  with this change
- most of the kernel code will not care about the actual encoding of
  scope zone IDs and won't touch "s6_addr16[1]" directly.
- similarly, most of the kernel code will not care about link-local
  scoped addresses as a special case.
- scope boundary check will be stricter.  For example, the current
  *BSD code allows a packet with src=::1 and dst=(some global IPv6
  address) to be sent outside of the node, if the application do:
    s = socket(AF_INET6);
    bind(s, "::1");
    sendto(s, some_global_IPv6_addr);
  This is clearly wrong, since ::1 is only meaningful within a single
  node, but the current implementation of the *BSD kernel cannot
  reject this attempt.

Submitted by:	JINMEI Tatuya <jinmei__at__isl.rdc.toshiba.co.jp>
Obtained from:	KAME