netinet6: Add sysctl flag CTLFLAG_TUN to loader tunables
The following sysctl variables are actually loader tunables. Add sysctl
flag CTLFLAG_TUN to them so that sysctl -T will report them correctly.
- net.inet6.ip6.auto_linklocal
- net.inet6.ip6.accept_rtadv
- net.inet6.ip6.no_radr
No functional change intended.
Reviewed by: glebius
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D41928