[nrf fromtree] net: shell: Fix CI warning implicit declaration

Fixes "implicit declaration of function ARRAY_SIZE"
observed during CI.

Signed-off-by: Ajay Parida <[email protected]>
(cherry picked from commit f519b4d)

Author: ajayparida

include/zephyr/net/wifi.h

@@ -12,6 +12,8 @@
 #ifndef ZEPHYR_INCLUDE_NET_WIFI_H_
 #define ZEPHYR_INCLUDE_NET_WIFI_H_
 
+#include <zephyr/sys/util.h>  /* for ARRAY_SIZE */
+
 #define WIFI_COUNTRY_CODE_LEN 2
 
 /* Not having support for legacy types is deliberate to enforce