face: Expose ioService from Node and Face.

Change-Id: Id682908603902f378ba534694b4dc6db6fdd7ca3
diff --git a/src/face.hpp b/src/face.hpp
index 61d872f..a757061 100644
--- a/src/face.hpp
+++ b/src/face.hpp
@@ -197,6 +197,9 @@
    */
   void 
   shutdown();
+
+  shared_ptr<boost::asio::io_service> 
+  ioService() { return node_.ioService(); }
   
 private:
   Node node_;
diff --git a/src/node.hpp b/src/node.hpp
index 7892075..6dc1954 100644
--- a/src/node.hpp
+++ b/src/node.hpp
@@ -147,6 +147,9 @@
   void 
   shutdown();
 
+  shared_ptr<boost::asio::io_service> 
+  ioService() { return ioService_; }
+
 private:
   void
   asyncExpressInterest(const ptr_lib::shared_ptr<const Interest> &interest,