[NET]: Avoid atomic xchg() for non-error case

It also looks like there were 2 places where the test on sk_err was
missing from the event wait logic (in sk_stream_wait_connect and
sk_stream_wait_memory), while the rest of the sock_error() users look
to be doing the right thing.  This version of the patch fixes those,
and cleans up a few places that were testing ->sk_err directly.

Signed-off-by: Benjamin LaHaise <benjamin.c.lahaise@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 9cb00dc..6481814 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -637,8 +637,9 @@
 
 	BT_DBG("sock %p, sk %p", sock, sk);
 
-	if (sk->sk_err)
-		return sock_error(sk);
+	err = sock_error(sk);
+	if (err)
+		return err;
 
 	if (msg->msg_flags & MSG_OOB)
 		return -EOPNOTSUPP;