net: correct off-by-one write allocations reports

commit 2b85a34e911bf483c27cfdd124aeb1605145dc80
(net: No more expensive sock_hold()/sock_put() on each tx)
changed initial sk_wmem_alloc value.

We need to take into account this offset when reporting
sk_wmem_alloc to user, in PROC_FS files or various
ioctls (SIOCOUTQ/TIOCOUTQ)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index f7a53b2..590b839 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1748,8 +1748,7 @@
 	switch (cmd) {
 		/* Protocol layer */
 		case TIOCOUTQ: {
-			long amount = sk->sk_sndbuf -
-				      atomic_read(&sk->sk_wmem_alloc);
+			long amount = sk->sk_sndbuf - sk_wmem_alloc_get(sk);
 
 			if (amount < 0)
 				amount = 0;