Bump up twisted's thread pool size

Change-Id: Ib56be8224fed1a317ab2bee30471e8c8113ffa3f
diff --git a/ofagent/main.py b/ofagent/main.py
index 371d26a..608e1e4 100755
--- a/ofagent/main.py
+++ b/ofagent/main.py
@@ -262,6 +262,7 @@
 
         reactor.addSystemEventTrigger('before', 'shutdown',
                                       self.shutdown_components)
+        reactor.suggestThreadPoolSize(30)
         reactor.run()