tcp: stamp SCM_TSTAMP_ACK later in tcp_clean_rtx_queue()

Currently tp->delivered is updated with sacked packets but not
cumulatively acked when SCP_TSTAMP_ACK is timestamped. This patch moves
a tcp_ack_tstamp() call in tcp_clean_rtx_queue() to later in the loop so
that when a skb is fully acked OPT_STATS of SCM_TSTAMP_ACK will include
the current skb in the delivered count. When not fully acked
tcp_ack_tstamp() is a no-op and there is no change in behavior.

Signed-off-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>