Disable Nageling on TCP clients

Nageling, due to the nature of keep-alive connections, slows them down
considerably, especially on Linux. On Linux, a 500ms delay is introduced
when sending back the last packet of a response over a persistent
connection.

This option was tested on OS X and showed minimal effect to performance.

lib/puma/server.rb

@@ -126,6 +126,10 @@ module Puma
     end
 
     def process_client(client)
+      if client.kind_of? TCPSocket
+        client.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
+      end
+
       begin
         while true
           parser = HttpParser.new