link/inet6: add support for tokenized interface identifiers

http://tools.ietf.org/html/draft-chown-6man-tokenised-ipv6-identifiers-02

[thaller@redhat.com: Add OOM handling, fix whitespace issues]

https://github.com/thom311/libnl/pull/63

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Thomas Haller <thaller@redhat.com>