u2k15: florian@ on IPv6 hackery

The next hackathon report is from Florian Obser (florian@), who writes:

I'm not entirely sure if mg(1) has dedicated maintainers, but if there are it's probably lum@,
jasper@ and me. When u2k15 was first discussed at c2k15 in Calgary someone said:
"Florian, will you come? We need utf8 for mg!"
Me: "For sure I will come, I will build myself an IT throne and mock anybody who touches mg(1)'s
input handling."

But seriously, I do agree that mg(1) needs to understand utf8, but I'm not
competent (at this time) to make this happen. I try to follow along what's
going on with utf8, but for u2k15 I joined the network hackers.

phessler@ and claudio@ introduced the concept of an emergency hackathon at
g2k14, and I went with that option: Fly in on Friday evening and leave at
stupid o'clock on Monday. It became blatantly obvious that my traveling
would be quite different from my c2k15 experience when I asked for a beer
on the flight and got handed a Heineken...

At the hackathon I continued poking ping(8) and ping6(8) to see what would
stick to eventually merge the two into one binary. This led to the -g
option in ping6(8). Which then led to the removal of IPV6_NEXTHOP support
from the kernel to the great joy of mpi@. Source routing isn't considered
to be a good idea these days, or as claudio@ pointed out, it wasn't a good
idea 20 years ago.

mpi@ then pointed out that linkmtu and maxmtu from struct nd_ifinfo and
more importantly the IN6_LINKMTU macro were getting in his way. Handling
the mtu in the kernel on a received router advertisement message doesn't
seem to be the right way to handle this. I think this was the first
hackathon where I commited a net minus...

˙uǝddɐɥ uoɥʇɐʞɔɐɥ sıɥʇ ƃuıʞɐɯ ɹoɟ ǝsʃǝ ʎpoqʎɹǝʌǝ puɐ uıʃɹǝq-uı '@ǝʍn '@dsʇs oʇ sʞuɐɥʇ

Thanks for the deep probe in the code and the report, Florian!