This patch fixes the following issues:

This patch fixes the following issues:
- Interface link-local address is not reachable within the
  node that owns the interface, this is due to the mismatch
  in address scope as the result of the installed interface
  address loopback route. Therefore for each interface
  address loopback route, the rt_gateway field (of AF_LINK
  type) will be used to track which interface a given
  address belongs to. This will aid the address source to
  use the proper interface for address scope/zone validation.
- The loopback address is not reachable. The root cause is
  the same as the above.
- Empty nd6 entries are created for the IPv6 loopback addresses
  only for validation reason. Doing so will eliminate as much
  of the special case (loopback addresses) handling code
  as possible, however, these empty nd6 entries should not
  be returned to the userland applications such as the
  "ndp" command.
Since both of the above issues contain common files, these
files are committed together.

Reviewed by:	bz
MFC after:	immediately