net: annotate accesses to dev->gso_max_size

dev->gso_max_size is written under RTNL protection, or when the device is
not yet visible, but is read locklessly.

Add the READ_ONCE()/WRITE_ONCE() pairs, and use netif_set_gso_max_size()
where we can to better document what is going on.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index 64b2d4f..d3e1c22 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -525,7 +525,7 @@ static void br_set_gso_limits(struct net_bridge *br)
 		gso_max_size = min(gso_max_size, p->dev->gso_max_size);
 		gso_max_segs = min(gso_max_segs, p->dev->gso_max_segs);
 	}
-	br->dev->gso_max_size = gso_max_size;
+	netif_set_gso_max_size(br->dev, gso_max_size);
 	br->dev->gso_max_segs = gso_max_segs;
 }