batman-adv: Split a condition check

Let us split a check for a condition at the beginning of the
batadv_is_ap_isolated() function so that a direct return can be performed
in this function if the variable "vlan" contained a null pointer.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

net/batman-adv/translation-table.c

@@ -3339,7 +3339,10 @@ bool batadv_is_ap_isolated(struct batadv_priv *bat_priv, u8 *src, u8 *dst,
 	bool ret = false;
 
 	vlan = batadv_softif_vlan_get(bat_priv, vid);
-	if (!vlan || !atomic_read(&vlan->ap_isolation))
+	if (!vlan)
+		return false;
+
+	if (!atomic_read(&vlan->ap_isolation))
 		goto out;
 
 	tt_local_entry = batadv_tt_local_hash_find(bat_priv, dst, vid);