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/ieee802154/dgram.c b/net/ieee802154/dgram.c
index 1779677..14d3984 100644
--- a/net/ieee802154/dgram.c
+++ b/net/ieee802154/dgram.c
@@ -126,7 +126,8 @@
 	switch (cmd) {
 	case SIOCOUTQ:
 	{
-		int amount = atomic_read(&sk->sk_wmem_alloc);
+		int amount = sk_wmem_alloc_get(sk);
+
 		return put_user(amount, (int __user *)arg);
 	}