netinet6: store ND context directly in struct in6_ifextra

[glebius]

Summary

Stop using struct nd_ifinfo for that, because it is an API struct for
SIOCGIFINFO_IN6. The functional changes are isolated to the protocol
attach and detach: in6_ifarrival(), nd6_ifattach(), in6_ifdeparture(),
nd6_ifdetach(), as well as to the nd6_ioctl(), nd6_ra_input(),
nd6_slowtimo() and in6_ifmtu().

The dad_failures member was just renamed to match the rest. The M_IP6NDP
malloc(9) type declaration moved to files that actually use it.

The rest of the changes are mechanical substitution of double pointer
dereference via ND_IFINFO() to a single pointer dereference. This was
achieved with a sed(1) script:

s/ND_IFINFO\(([a-z0-9>_.-]+)\)->(flags|linkmtu|basereachable|reachable|retrans|chlim)/\1->if_inet6->nd_\2/g
s/nd_chlim/nd_curhoplimit/g

[madpilot]

Looks fine to me

[tuexen]

sys/netinet6/in6.c

2632–2633

Maybe use something like:

	const uint32_t linkmtu = ifp->if_inet6->nd_linkmtu;
	const uint32_t maxmtu = ifp->if_inet6->nd_maxmtu;
	const uint32_t if_mtu = ifp->if_inet6->if_mtu;

For me that is more readable and possibly more inline with style.9. But I leave that up to you.

2634

Maybe:

if (linkmtu > 0 && linkmtu < ifmtu)
	return (linkmtu);
if (maxmtu > 0 && maxmtu < ifmtu)
	return (maxmtu);
return (ifmtu);

is more easier to read. But I leave that also up to you.

[glebius]

In in6_ifmtu() unroll the two level ternary operator into a more readable form.