Anand Parthasarathy pointed out that draft-ietf-ipoib-ip-over-infiniband-09.txt says:

            [DISC] specifies the length of source/target option in
            number of 8-octets as indicated by a length of '3' above.
            Since the IPoIB link-layer address is only 20-octet long,
            two octets of zero MUST be prepended to fill the total
            option length of 24 octets.

The current Linux neighbour discovery code puts the padding after the
link address.  This patch fixes up ndisc.c to put the padding in the
correct place by adding a general ndisc_addr_option_pad() function
(which could be used in the future if someone ever implements RFC 3831
IPv6-over-FC or some other encapsulation that requires padding).
Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>