ipv4: dccp: handle ICMP messages on DCCP_NEW_SYN_RECV request sockets

dccp_v4_err() can restrict lookups to ehash table, and not to listeners.

Note this patch creates the infrastructure, but this means that ICMP
messages for request sockets are ignored until complete conversion.

New dccp_req_err() helper is exported so that we can use it in IPv6
in following patch.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 2396f50..bebc735 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -317,6 +317,7 @@
 unsigned int dccp_poll(struct file *file, struct socket *sock,
 		       poll_table *wait);
 int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
+void dccp_req_err(struct sock *sk, u64 seq);
 
 struct sk_buff *dccp_ctl_make_reset(struct sock *sk, struct sk_buff *skb);
 int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code);