interest: Allow in-wire refreshing of Interest's nonce

Change-Id: I47500fce16a1d37af865d3f9dab59355d6108c95
Refs: #1758
diff --git a/src/interest.hpp b/src/interest.hpp
index 0750542..89c5c24 100644
--- a/src/interest.hpp
+++ b/src/interest.hpp
@@ -334,6 +334,17 @@
   Interest&
   setNonce(uint32_t nonce);
 
+  /**
+   * @brief Refresh nonce
+   *
+   * Refresh guarantees that new nonce value is different from the existing one.
+   *
+   * If nonce is already set, it will be updated to a different random value.
+   * If nonce is not set, this method will do nothing.
+   */
+  void
+  refreshNonce();
+
   //
 
   nfd::LocalControlHeader&