Thomas Haller authored Apr 29, 2016 and Lubomir Rintel committed May 30, 2016

The only user of platform who accesses this field is NMDevice,
when calling nm_platform_link_get_ipv6_token(). It cares more
about whether the token is all-zero or set to something.

Another use of inet6_token.is_valid was so that when we receive a
netlink message without IFLA_INET6_TOKEN attribute, that we don't
treat the value as zero, although it is just unknown. Fix that
instead in a better way by setting the value from the cache, if
IFLA_AF_SPEC doesn't provide it.

Also, when printing the token in nm_platform_link_to_string()
treat it as an IPv6 address (inet_ntop).