bridge: inherit slave devices needed_headroom

Some slave devices may have set a dev->needed_headroom value which is
different than the default one, most likely in order to prepend a
hardware descriptor in front of the Ethernet frame to send. Whenever a
new slave is added to a bridge, ensure that we update the
needed_headroom value accordingly to account for the slave
needed_headroom value.
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_if.c

@@ -383,6 +383,9 @@ int br_add_if(struct net_bridge *br, struct net_device *dev)
 
 	netdev_update_features(br->dev);
 
+	if (br->dev->needed_headroom < dev->needed_headroom)
+		br->dev->needed_headroom = dev->needed_headroom;
+
 	spin_lock_bh(&br->lock);
 	changed_addr = br_stp_recalculate_bridge_id(br);