libndp: validate the IPv6 hop limit
libndp: validate the IPv6 hop limit

None of the NDP messages should ever come from a non-local network; as
stated in RFC4861's 6.1.1 (RS), 6.1.2 (RA), 7.1.1 (NS), 7.1.2 (NA),
and 8.1. (redirect):

  - The IP Hop Limit field has a value of 255, i.e., the packet
    could not possibly have been forwarded by a router.

This fixes CVE-2016-3698.

Reported by: Julien BERNARD <julien.bernard@viagenie.ca>
Signed-off-by: Lubomir Rintel <c9b9bbc6e9b0bc7e9cec5af1551c7b98adb9530c@v3.sk>
Signed-off-by: Jiri Pirko <1b548d10035ae428195c41f5d55eedb1437ccd8a@mellanox.com>

jpirko/libndp,jpirko/libndp,AGWA/libndp-debian,AGWA/libndp-debian