udp/client: Define ClientData constructor/destructor in cpp file

Prevents compilation errors on clang 12 due to incomplete types within a
unique_ptr member.

src/input_common/udp/client.cpp

@@ -144,6 +144,10 @@ Client::~Client() {
     Reset();
 }
 
+Client::ClientData::ClientData() = default;
+
+Client::ClientData::~ClientData() = default;
+
 std::vector<Common::ParamPackage> Client::GetInputDevices() const {
     std::vector<Common::ParamPackage> devices;
     for (std::size_t client = 0; client < clients.size(); client++) {

src/input_common/udp/client.h

@@ -98,6 +98,9 @@ public:
 
 private:
     struct ClientData {
+        ClientData();
+        ~ClientData();
+
         std::string host{"127.0.0.1"};
         u16 port{26760};
         std::size_t pad_index{};