Guard spec which only works on Linux

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64465 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/library/socket/addrinfo/initialize_spec.rb

@@ -447,7 +447,7 @@ describe "Addrinfo#initialize" do
         end
       end
 
-      platform_is_not :windows, :solaris do
+      platform_is :linux do
         describe 'and the socket type is set to SOCK_SEQPACKET' do
           before do
             @socktype = Socket::SOCK_SEQPACKET