libndb: reject redirect and router advertisements from non-link-local

RFC4861 suggests that these messages should only originate from
link-local addresses in 6.1.2 (RA) and 8.1. (redirect):

Mitigates CVE-2016-3698.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>