netpoll: copy dev name of slaves to struct netpoll

Otherwise we will not see the name of the slave dev in error
message:

[  388.469446] (null):  doesn't support polling, aborting.

Signed-off-by: WANG Cong <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index a6b2f86..c188c80 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -243,6 +243,7 @@
 		goto out;
 
 	np->dev = p->dev;
+	strlcpy(np->dev_name, p->dev->name, IFNAMSIZ);
 
 	err = __netpoll_setup(np);
 	if (err) {