network: NIC spoof (#911)

## Link to GitHub Issue or related Pull Request, if one exists
#0

## Description of change
Spoof a valid NIC, so games can use a local server completely offline.
Previously this was impossible on macOS wine, or it required km-test
loopback adapter on Windows.

## Testing
Tested DDR (32bit/64bit) and SDVX on Windows 10 and macOS Tahoe.
Enabling -nicspoof and -icmphook connects to airgapped 127.0.0.1.

src/spice2x/launcher/options.h

@@ -316,6 +316,7 @@ namespace launcher {
             OtocaCamHook,
             DisableHighResTimer,
             EnableICMPHook,
+            EnableNICSpoof,
             AutoElevate,
             CfgForceSoftwareRender,
             OBSWebSocketEnabled,