hostapd: add missing return code for the bss_mgmt_enable ubus method

Fixes bogus errors on ubus calls

Signed-off-by: Felix Fietkau <nbd@nbd.name>
(cherry picked from commit cf992ca862)

package/network/services/hostapd/src/src/ap/ubus.c

@@ -1097,6 +1097,8 @@ hostapd_bss_mgmt_enable(struct ubus_context *ctx, struct ubus_object *obj,
 	}
 
 	__hostapd_bss_mgmt_enable(hapd, flags);
+
+	return 0;
 }