core: Add function to reset the next random variable stream index counter

src/core/model/rng-seed-manager.cc

@@ -101,4 +101,10 @@ RngSeedManager::GetNextStreamIndex()
     return next;
 }
 
+void
+RngSeedManager::ResetNextStreamIndex()
+{
+    g_nextStreamIndex = 0;
+}
+
 } // namespace ns3

src/core/model/rng-seed-manager.h

@@ -93,6 +93,11 @@ class RngSeedManager
      * \returns The next stream index.
      */
     static uint64_t GetNextStreamIndex();
+
+    /**
+     * Resets the global stream index counter.
+     */
+    static void ResetNextStreamIndex();
 };
 
 /** Alias for compatibility. */