-Open socket() at first and then setuid() to actual user.
-Allow ping6 preload option only for root.
Approved by: jkh
Submitted by: Neil Blakey-Milner <nbm@mithrandr.moria.org>
getipnodebyaddr().
This resolve 2 problems.
-can specify scope index(@ifname) for IPv6 link local addr
-reverse lookup for IPv6 loopback addr(::1) was strange, but fixed