Also fixes ping tests. Latest Linux kernels prohibit to access ICMPv6
properties with non-privileged sockets.

Fixes golang/go#12163.

Change-Id: I439b41556e8d4c2f3a9f725131267469e08c9599
Reviewed-on: https://go-review.googlesource.com/13653Reviewed-by: Ian Lance Taylor <iant@golang.org>