samples: wifi: radio_test: Wait for driver initialization to complete

As the sample use global variables of driver, add checks and wait for
driver initialization to complete to avoid crashes if the sample starts
too early or driver initialization gets delayed.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

samples/wifi/radio_test/src/nrf_wifi_radio_test_shell.c

@@ -16,6 +16,7 @@
 extern struct wifi_nrf_drv_priv_zep rpu_drv_priv_zep;
 struct wifi_nrf_ctx_zep *ctx = &rpu_drv_priv_zep.rpu_ctx_zep;
 
+#define NRF_WIFI_RADIO_TEST_INIT_TIMEOUT_MS 5000
 
 static bool check_test_in_prog(const struct shell *shell)
 {
@@ -2432,6 +2433,18 @@ SHELL_CMD_REGISTER(wifi_radio_test,
 static int nrf_wifi_radio_test_shell_init(void)
 {
 	enum wifi_nrf_status status = WIFI_NRF_STATUS_FAIL;
+	unsigned int timeout = 0;
+
+	while (!ctx->rpu_ctx && timeout < NRF_WIFI_RADIO_TEST_INIT_TIMEOUT_MS) {
+		k_sleep(K_MSEC(100));
+		timeout += 100;
+	}
+
+	if (!ctx->rpu_ctx) {
+		printf("nRF Wi-Fi radio test shell init timedout waiting for driver: %d\n",
+		       NRF_WIFI_RADIO_TEST_INIT_TIMEOUT_MS);
+		return -ENOEXEC;
+	}
 
 	status = nrf_wifi_radio_test_conf_init(&ctx->conf_params);