Prefer matching labels and longest matching prefix

...when performing source address selection for IPv6.

These are defined in RFC 6724 section 5 rule 6 (prefer matching label)
and rule 8 (use longest matching prefix).

This change also considers ULA of global scope instead of its own scope,
as per RFC 6724 section 3.1:

   Also, note that ULAs are considered as global, not
   site-local, scope but are handled via the prefix policy table as
   discussed in Section 10.6.

Test: stack_test.TestIPv6SourceAddressSelectionScope

Startblock:
  has LGTM from peterjohnston
  and then
  add reviewer brunodalbo
PiperOrigin-RevId: 348580996

0 files changed, 0 insertions, 0 deletions