bridge/mdb: remove wrong use of NLM_F_MULTI

commit 82199679 upstream.

NLM_F_MULTI must be used only when a NLMSG_DONE message is sent. In fact,
it is sent only at the end of a dump.

Libraries like libnl will wait forever for NLMSG_DONE.

Fixes: 37a393bc ("bridge: notify mdb changes via netlink")
CC: Cong Wang <amwang@redhat.com>
CC: Stephen Hemminger <stephen@networkplumber.org>
CC: bridge@lists.linux-foundation.org
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/bridge/br_mdb.c

@@ -170,7 +170,7 @@ static int nlmsg_populate_mdb_fill(struct sk_buff *skb,
 	struct br_port_msg *bpm;
 	struct nlattr *nest, *nest2;
 
-	nlh = nlmsg_put(skb, pid, seq, type, sizeof(*bpm), NLM_F_MULTI);
+	nlh = nlmsg_put(skb, pid, seq, type, sizeof(*bpm), 0);
 	if (!nlh)
 		return -EMSGSIZE;