dccp: consistently use dccp_write_space()

DCCP uses dccp_write_space() for sk->sk_write_space method.

Unfortunately a passive connection (as provided by accept())
is using the generic sk_stream_write_space() function.

Lets simply inherit sk->sk_write_space from the parent
instead of forcing the generic one.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Cc: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/inet_connection_sock.c

@@ -790,7 +790,6 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
 		inet_sk(newsk)->inet_dport = inet_rsk(req)->ir_rmt_port;
 		inet_sk(newsk)->inet_num = inet_rsk(req)->ir_num;
 		inet_sk(newsk)->inet_sport = htons(inet_rsk(req)->ir_num);
-		newsk->sk_write_space = sk_stream_write_space;
 
 		/* listeners have SOCK_RCU_FREE, not the children */
 		sock_reset_flag(newsk, SOCK_RCU_FREE);