face: Fix bug with removePendingInterest

Change-Id: I364c1441da2cc0042ba461bc3a6cb4b70e53b166
Refs: #1917
diff --git a/src/face.hpp b/src/face.hpp
index 974aa69..3407d92 100644
--- a/src/face.hpp
+++ b/src/face.hpp
@@ -225,6 +225,12 @@
   removePendingInterest(const PendingInterestId* pendingInterestId);
 
   /**
+   * @brief Get number of pending Interests
+   */
+  size_t
+  getNPendingInterests() const;
+
+  /**
    * @brief Set InterestFilter to dispatch incoming matching interest to onInterest
    * callback and register the filtered prefix with the connected NDN forwarder
    *