gui.c: fix macOS build - stop undefining htons/htonl
On macOS htons/htonl exist only as macros, so the #undef left no declaration and GCC 14+ treats the implicit declaration as an error. Drop the #undefs and include <arpa/inet.h> instead.
Authored by: mikeaubury 4 days ago
Parent: [r13210]
Child: [r13212]