link: update copy of kernel header include/linux/if_link.h

The next patch will use some of these defines, so update.

Taken from upstream kernel commit bc91b0f07ada5535427373a4e2050877bcc12218,
file 'include/uapi/linux/if_link.h'.

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Thomas Haller <thaller@redhat.com>
link/inet6: add link IPv6 address generation mode support

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Thomas Haller <thaller@redhat.com>
fixup! inet6: add link IPv6 address generation mode support