nd6_lookup prints bogus messages with point to point devices

[George V. Neville-Neil]

Hi,

After way too long this has been tested and committed to HEAD, with an
MFC timout of 1 week.  I have done only limited, aka, ping, testing of
this fix.

I am currently setting up my own outbound IPv6 network so that I can
do more real world testing of such patches in future.

Later,
George