LibCore+LookupServer: Implement and use UDPServer::send

Author: https://github.com/sin-ack
Commit: 0cca6cef95
Pull-request: https://github.com/SerenityOS/serenity/pull/9977
Reviewed-by: https://github.com/Dexesttp
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibCore/UDPServer.h

@@ -30,6 +30,8 @@ public:
         return receive(size, saddr);
     };
 
+    ErrorOr<size_t> send(ReadonlyBytes, sockaddr_in const& to);
+
     Optional<IPv4Address> local_address() const;
     Optional<u16> local_port() const;