IP4: add any_ip constant for all ones

esp32/max80/IP4.h

@@ -64,4 +64,5 @@ public:
     const char *cstr();
 };
 
-constexpr IP4 null_ip(0);
+constexpr IP4 null_ip((uint32_t)0);
+constexpr IP4 any_ip(~(uint32_t)0);