net: rename SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA

This patch is a cleanup to make following patch easier to
review.

Goal is to move SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA
from (struct socket)->flags to a (struct socket_wq)->flags
to benefit from RCU protection in sock_wake_async()

To ease backports, we rename both constants.

Two new helpers, sk_set_bit(int nr, struct sock *sk)
and sk_clear_bit(int net, struct sock *sk) are added so that
following patch can change their implementation.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/stream.c b/net/core/stream.c
index d70f77a0..4330942 100644
--- a/net/core/stream.c
+++ b/net/core/stream.c
@@ -126,7 +126,7 @@
 		current_timeo = vm_wait = (prandom_u32() % (HZ / 5)) + 2;
 
 	while (1) {
-		set_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
+		sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
 
 		prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
 
@@ -139,7 +139,7 @@
 		}
 		if (signal_pending(current))
 			goto do_interrupted;
-		clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
+		sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
 		if (sk_stream_memory_free(sk) && !vm_wait)
 			break;