Move CaptureMessageToFile() declaration from header to implementation

src/net.cpp

@@ -2915,7 +2915,8 @@ uint64_t CConnman::CalculateKeyedNetGroup(const CAddress& address) const
     return GetDeterministicRandomizer(RANDOMIZER_ID_NETGROUP).Write(vchNetGroup.data(), vchNetGroup.size()).Finalize();
 }
 
-void CaptureMessageToFile(const CAddress& addr,
+// Dump binary message to file, with timestamp.
+static void CaptureMessageToFile(const CAddress& addr,
                                  const std::string& msg_type,
                                  Span<const unsigned char> data,
                                  bool is_incoming)

src/net.h

@@ -1221,12 +1221,6 @@ private:
     friend struct ConnmanTestMsg;
 };
 
-/** Dump binary message to file, with timestamp */
-void CaptureMessageToFile(const CAddress& addr,
-                          const std::string& msg_type,
-                          Span<const unsigned char> data,
-                          bool is_incoming);
-
 /** Defaults to `CaptureMessageToFile()`, but can be overridden by unit tests. */
 extern std::function<void(const CAddress& addr,
                           const std::string& msg_type,