batman-adv: Delete an unnecessary check before the function call "batadv_softif_vlan_free_ref"

The batadv_softif_vlan_free_ref() function tests whether its argument is NULL
and then returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.
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

@@ -3356,7 +3356,6 @@ bool batadv_is_ap_isolated(struct batadv_priv *bat_priv, u8 *src, u8 *dst,
 	ret = true;
 
 out:
-	if (vlan)
 	batadv_softif_vlan_free_ref(vlan);
 	if (tt_global_entry)
 		batadv_tt_global_entry_free_ref(tt_global_entry);