netpoll: use GFP_ATOMIC in slave_enable_netpoll() and __netpoll_setup()

slave_enable_netpoll() and __netpoll_setup() may be called
with read_lock() held, so should use GFP_ATOMIC to allocate
memory. Eric suggested to pass gfp flags to __netpoll_setup().

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Cong Wang <amwang@redhat.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 e1144e1..171fd6b 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -361,7 +361,7 @@
 	if (err)
 		goto err2;
 
-	if (br_netpoll_info(br) && ((err = br_netpoll_enable(p))))
+	if (br_netpoll_info(br) && ((err = br_netpoll_enable(p, GFP_KERNEL))))
 		goto err3;
 
 	err = netdev_set_master(dev, br->dev);