spec/ruby/library/socket/socket/getaddrinfo_spec.rb: avoid nonsensical lookup

"http" is a TCP service, so /etc/services on typical GNU/Linux systems
only specify a TCP port for it.  Use "discard" since it seems
used for other specs and is specified as both TCP and UDP.

This caused many CI failures like the following:
  git clone https://gist.github.com/812a9b747e4c4cb2e844d4be7991cd2d

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64181 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/library/socket/socket/getaddrinfo_spec.rb

@@ -278,11 +278,11 @@ describe 'Socket.getaddrinfo' do
 
     platform_is_not :windows do
       it 'accepts a Fixnum as the protocol family' do
-        addr = Socket.getaddrinfo(nil, 'http', :INET, :DGRAM, Socket::IPPROTO_UDP)
+        addr = Socket.getaddrinfo(nil, 'discard', :INET, :DGRAM, Socket::IPPROTO_UDP)
 
         addr[0].should == [
           'AF_INET',
-          80,
+          9,
           '127.0.0.1',
           '127.0.0.1',
           Socket::AF_INET,