esp32/mpconfigport.h: Seed the urandom module on import.

For seeding, the RNG function of the ESP-IDF is used, which is told to be a
true RNG, at least when WiFi or Bluetooth is enabled.  Seeding on import is
as per CPython.  To obtain a reproducible sequence of pseudo-random numbers
one must explicitly seed with a known value.

ports/esp32/mpconfigport.h

@@ -6,6 +6,7 @@
 
 #include <stdint.h>
 #include <alloca.h>
+#include "esp_system.h"
 
 #if !MICROPY_ESP_IDF_4
 #include "rom/ets_sys.h"
@@ -141,6 +142,7 @@
 #define MICROPY_PY_UBINASCII_CRC32          (1)
 #define MICROPY_PY_URANDOM                  (1)
 #define MICROPY_PY_URANDOM_EXTRA_FUNCS      (1)
+#define MICROPY_PY_URANDOM_SEED_INIT_FUNC   (esp_random())
 #define MICROPY_PY_OS_DUPTERM               (1)
 #define MICROPY_PY_MACHINE                  (1)
 #define MICROPY_PY_MACHINE_PIN_MAKE_NEW     mp_pin_make_new