Separate out GetExternalIPAddress helper function

De-duplicates the two inline implementations and prepares it for use from Android.

Source/Core/Core/NetPlayCommon.cpp

@@ -9,6 +9,7 @@
 #include <lzo/lzo1x.h>
 
 #include "Common/FileUtil.h"
+#include "Common/HttpRequest.h"
 #include "Common/IOFile.h"
 #include "Common/MsgHandler.h"
 #include "Common/SFMLHelper.h"
@@ -297,4 +298,18 @@ std::optional<std::vector<u8>> DecompressPacketIntoBuffer(sf::Packet& packet)
 
   return out_buffer;
 }
+
+std::string GetExternalIPAddress()
+{
+  Common::HttpRequest request;
+  // ENet does not support IPv6, so IPv4 has to be used
+  request.UseIPv4();
+  Common::HttpRequest::Response response =
+      request.Get("https://ip.dolphin-emu.org/", {{"X-Is-Dolphin", "1"}});
+
+  if (response.has_value())
+    return std::string(response->begin(), response->end());
+  return "";
+}
+
 }  // namespace NetPlay

Source/Core/Core/NetPlayCommon.h

@@ -20,6 +20,8 @@ using namespace std::chrono_literals;
 // connection is disconnected
 constexpr std::chrono::milliseconds PEER_TIMEOUT = 30s;
 
+std::string GetExternalIPAddress();
+
 bool CompressFileIntoPacket(const std::string& file_path, sf::Packet& packet);
 bool CompressFolderIntoPacket(const std::string& folder_path, sf::Packet& packet);
 bool CompressBufferIntoPacket(std::span<const u8> in_buffer, sf::Packet& packet);

Source/Core/Core/NetPlayServer.cpp

@@ -24,7 +24,6 @@
 #include "Common/CommonPaths.h"
 #include "Common/ENet.h"
 #include "Common/FileUtil.h"
-#include "Common/HttpRequest.h"
 #include "Common/Logging/Log.h"
 #include "Common/MsgHandler.h"
 #include "Common/SFMLHelper.h"
@@ -220,16 +219,9 @@ void NetPlayServer::SetupIndex()
   }
   else
   {
-    Common::HttpRequest request;
-    // ENet does not support IPv6, so IPv4 has to be used
-    request.UseIPv4();
-    Common::HttpRequest::Response response =
-        request.Get("https://ip.dolphin-emu.org/", {{"X-Is-Dolphin", "1"}});
-
-    if (!response.has_value())
+    session.server_id = GetExternalIPAddress();
+    if (session.server_id.empty())
       return;
-
-    session.server_id = std::string(response->begin(), response->end());
   }
 
   session.EncryptID(Config::Get(Config::NETPLAY_INDEX_PASSWORD));

Source/Core/DolphinQt/NetPlay/NetPlayDialog.cpp

@@ -30,7 +30,7 @@
 #endif
 
 #include "Common/Config/Config.h"
-#include "Common/HttpRequest.h"
+#include "Core/NetPlayCommon.h"
 #include "Common/Logging/Log.h"
 #include "Common/TraversalClient.h"
 
@@ -550,17 +550,8 @@ void NetPlayDialog::show(std::string nickname, bool use_traversal)
 
 void NetPlayDialog::ResetExternalIP()
 {
-  m_external_ip_address = Common::Lazy<std::string>([]() -> std::string {
-    Common::HttpRequest request;
-    // ENet does not support IPv6, so IPv4 has to be used
-    request.UseIPv4();
-    Common::HttpRequest::Response response =
-        request.Get("https://ip.dolphin-emu.org/", {{"X-Is-Dolphin", "1"}});
-
-    if (response.has_value())
-      return std::string(response->begin(), response->end());
-    return "";
-  });
+  m_external_ip_address =
+      Common::Lazy<std::string>([]() -> std::string { return NetPlay::GetExternalIPAddress(); });
 }
 
 void NetPlayDialog::UpdateDiscordPresence()