tests: support Linux kernels with CONFIG_IPV6=n
Detecting the presence of constants in C headers is insufficient, as a Linux kernel can be built with CONFIG_IPV6=n
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65055 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
tests: support Linux kernels with CONFIG_IPV6=n
Detecting the presence of constants in C headers is insufficient,
as a Linux kernel can be built with CONFIG_IPV6=n
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65055 b2dd03c8-39d4-4d8f-98ff-823fe69b080e