HEADS UP: netstat needs to be updated

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

Hello -current users,

Running netstat -ia (before 2016-07-14) on a 7.99.35
(or newer) kernel causes a problem (same as PR kern/51325).
You can solve the problem by updating netstat with the
latest source code (or get a recent binary at
http://nyftp.netbsd.org/).

Technical details: netstat -ia used kvm(3) to get address
information from the kernel by reading lists of struct
in_ifaddr/in6_ifaddr embedding struct ifaddr. Since
2016-07-14, netstat -ia began to use sysctl instead of
kvm(3) to get the information. In favor of the change,
the kernel changed struct ifaddr (that was needed for
MP-safe network stack work) at 7.99.35, which broke
old netstat -ia.

The breakage is expected. We may not keep backcompat of
kvm(3) if the work for backcompat needs dirty workarounds
and/or extra overheads in the kernel.

Regards,
  ozaki-r