[nrf fromtree] wifi: shell: Fix default band value

The enum is mainly to print output of band, so, the default value is 0
which means 2.4GHz, which is not correct when using it to configure like
in connect.

Fix the default value to unknown i.e., no user preference. This way we
can use same enum for both set and get.

Signed-off-by: Chaitanya Tata <[email protected]>
(cherry picked from commit 8c17987)

Author: krish2718

subsys/net/l2/wifi/wifi_shell.c

@@ -341,6 +341,8 @@ static int __wifi_args_to_params(size_t argc, char *argv[],
 		return -EINVAL;
 	}
 
+	params->band = WIFI_FREQ_BAND_UNKNOWN;
+
 	/* SSID */
 	params->ssid = argv[0];
 	params->ssid_length = strlen(params->ssid);