Handle snd_una in tcp_cwnd_down()

Handle snd_una in tcp_cwnd_down()

commit 6ee8009e38006da81d2a53da1aaa27365552553e in mainline

Subject: [PATCH 1/1] [TCP]: Also handle snd_una changes in tcp_cwnd_down

tcp_cwnd_down must check for it too as it should be conservative
in case of collapse stuff and also when receiver is trying to
lie (though it wouldn't be successful anyway).

Note:
- Separated also is_dupack and do_lost in fast_retransalert
	* Much cleaner look-and-feel now
	* This time it really fixes cumulative ACK + many new
	  SACK blocks recovery entry (I claimed this fixes with
	  last patch but it wasn't). TCP will now call
	  tcp_update_scoreboard regardless of is_dupack when
	  in recovery as long as there is enough fackets_out.
- Introduce FLAG_SND_UNA_ADVANCED
	* Some prior_snd_una arguments are unnecessary after it
- Added helper FLAG_ANY_PROGRESS to avoid long FLAG...|FLAG...
  constructs

This is a reduced version of a mainline patch.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>