[TCP]: Receive buffer moderation fixes.

1) Make window clamp follow receive buffer growth so it
   does not limit window advertisements.  Noticed by John
   Heffner and Stephen Hemminger.
2) Fix rcvmem calculation such that tcp_adv_win_scale is
   taken into account.

net/ipv4/tcp_input.c

@@ -463,6 +463,8 @@ void tcp_rcv_space_adjust(struct sock *sk)
 		tp->rcvq_space.space = space;
 
 		if (sysctl_tcp_moderate_rcvbuf) {
+			int new_clamp = space;
+
 			/* Receive space grows, normalize in order to
 			 * take into account packet headers and sk_buff
 			 * structure overhead.
@@ -472,10 +474,16 @@ void tcp_rcv_space_adjust(struct sock *sk)
 				space = 1;
 			rcvmem = (tp->advmss + MAX_TCP_HEADER +
 				  16 + sizeof(struct sk_buff));
+			while (tcp_win_from_space(rcvmem) < tp->advmss)
+				rcvmem += 128;
 			space *= rcvmem;
 			space = min(space, sysctl_tcp_rmem[2]);
-			if (space > sk->sk_rcvbuf)
+			if (space > sk->sk_rcvbuf) {
 				sk->sk_rcvbuf = space;
+
+				/* Make the window clamp follow along.  */
+				tp->window_clamp = new_clamp;
+			}
 		}
 	}