batman-adv: Use bool as return type for boolean functions

It is easier to understand that the returned value of a specific function
doesn't have to be 0 when the functions was successful when the actual
return type is bool. This is especially true when all surrounding functions
with return type int use negative values to return the error code.

Reported-by: Nicholas Krause <xerofoify@gmail.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

net/batman-adv/hard-interface.c

@@ -146,22 +146,22 @@ static bool batadv_is_on_batman_iface(const struct net_device *net_dev)
 	return ret;
 }
 
-static int batadv_is_valid_iface(const struct net_device *net_dev)
+static bool batadv_is_valid_iface(const struct net_device *net_dev)
 {
 	if (net_dev->flags & IFF_LOOPBACK)
-		return 0;
+		return false;
 
 	if (net_dev->type != ARPHRD_ETHER)
-		return 0;
+		return false;
 
 	if (net_dev->addr_len != ETH_ALEN)
-		return 0;
+		return false;
 
 	/* no batman over batman */
 	if (batadv_is_on_batman_iface(net_dev))
-		return 0;
+		return false;
 
-	return 1;
+	return true;
 }
 
 /**
@@ -653,8 +653,7 @@ batadv_hardif_add_interface(struct net_device *net_dev)
 
 	ASSERT_RTNL();
 
-	ret = batadv_is_valid_iface(net_dev);
-	if (ret != 1)
+	if (!batadv_is_valid_iface(net_dev))
 		goto out;
 
 	dev_hold(net_dev);