When skb is coalesced tcp_ack_tstamp() still needs to be called when not
fully acked in tcp_clean_rtx_queue(), otherwise SCM_TSTAMP_ACK
timestamps may never be fired. Since the original patch series had
dependent commits, this patch fixes the issue instead of reverting by
restoring calls to tcp_ack_tstamp() when skb is not fully acked.

Fixes: fdb7eb21 ("tcp: stamp SCM_TSTAMP_ACK later in tcp_clean_rtx_queue()")
Signed-off-by: NYousuk Seung <ysseung@google.com>
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Acked-by: NSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>