network: icmp emulation (#694)

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

## Description of change
Add `-icmphook` option under spicecfg Development/Network for emulating
keepalive ping replies in user mode, so games do not need to open
privileged raw ICMP sockets. This makes connecting to networks possible
on macOS under Whisky, and on Windows with ICMP firewalled or spice
running without Administrator privileges.

## Testing
Tested DDR and SDVX on Windows 10 and macOS Tahoe. Network check status
in test menu shows `CONNECTED` when -icmphook is enabled, and `NOT
CONNECTED` when it is disabled. Actual network functionality works as
expected (under previously impossible conditions).

src/spice2x/launcher/launcher.cpp

@@ -76,6 +76,7 @@
 #include "hooks/graphics/graphics.h"
 #include "hooks/lang.h"
 #include "hooks/networkhook.h"
+#include "hooks/icmphook_net.h"
 #include "hooks/unisintrhook.h"
 #include "launcher/launcher.h"
 #include "launcher/logger.h"
@@ -244,6 +245,7 @@ int main_implementation(int argc, char *argv[]) {
     bool easrv_smart = false;
     bool load_stubs = false;
     bool netfix_disable = false;
+    bool icmphook_enable = false;
     bool lang_disable = false;
     std::string process_priority_str = "high";
     bool cardio_enabled = false;
@@ -732,6 +734,9 @@ int main_implementation(int argc, char *argv[]) {
     if (options[launcher::Options::DisableNetworkFixes].value_bool()) {
         netfix_disable = true;
     }
+    if (options[launcher::Options::EnableICMPHook].value_bool()) {
+        icmphook_enable = true;
+    }
     if (options[launcher::Options::DisableACPHook].value_bool()) {
         lang_disable = true;
     }
@@ -2259,6 +2264,11 @@ int main_implementation(int argc, char *argv[]) {
     avs::core::load_dll();
     avs::ea3::load_dll();
 
+    // ICMP emulation (opt-in; before games open raw ICMP sockets)
+    if (icmphook_enable) {
+        icmphook_net_init();
+    }
+
     // net fix
     if (!netfix_disable) {
         networkhook_init();