Add CConnmanTest to mutate g_connman in tests

src/net.h

@@ -431,6 +431,8 @@ private:
      *  in excess of nMaxOutbound
      *  This takes the place of a feeler connection */
     std::atomic_bool m_try_another_outbound_peer;
+
+    friend struct CConnmanTest;
 };
 extern std::unique_ptr<CConnman> g_connman;
 void Discover(boost::thread_group& threadGroup);