bridge/mdb: remove wrong use of NLM_F_MULTI

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

Libraries like libnl will wait forever for NLMSG_DONE.

Fixes: 949f1e39a617 ("bridge: mdb: notify on router port add and del")
CC: Nikolay Aleksandrov <[e-mail]>
Signed-off-by: Nicolas Dichtel <[e-mail]>
Acked-by: Nikolay Aleksandrov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/bridge/br_mdb.c

···
 	struct nlmsghdr *nlh;
 	struct nlattr *nest;
 
-	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;