NetServices: Implement controls on the number of concurrent requests.

This change allows the user to control how many concurrent request can be done
per session. This is going to be helpful to running the tests as well; they were
all fired up in parallel, which sometimes leads to our test server refusing a
connection.

Change-Id: I4f1f40b28b8e0199ea5589b36cd8d00ecd849a63

headers/private/netservices2/HttpSession.h

@@ -40,6 +40,10 @@ public:
 	void					Cancel(int32 identifier);
 	void					Cancel(const BHttpResult& request);
 
+	// Concurrency limits
+	void					SetMaxConnectionsPerHost(size_t maxConnections);
+	void					SetMaxHosts(size_t maxConnections);
+
 private:
 	struct Redirect;
 	class Request;