network: NIC spoof matching tunnel (#912)

## Link to GitHub Issue or related Pull Request, if one exists
#911

## Description of change
Add tunnelhost/tunnelclient modes to -nicspoof so two cabs can do
LAN-style BPL matching over a real UDP path (including Wine), while
keeping the fake overlay NIC. Offline spoof remains available as before.

## Testing
DDR

src/spice2x/CMakeLists.txt

@@ -617,6 +617,7 @@ set(SOURCE_FILES ${SOURCE_FILES}
         hooks/icmphook_net.cpp
         hooks/icmphook_iphlpapi.cpp
         hooks/nicspoof.cpp
+        hooks/nicspoof_tunnel.cpp
         hooks/powrprof.cpp
         #hooks/rom.cpp
         hooks/setupapihook.cpp