Merge branch 'tcp'

Yuchung Cheng says:

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This patch series improve RTT sampling in three ways:
1. Sample RTT during fast recovery and reordering events.
2. Favor ack-based RTT to timestamps because of broken TS ECR fields
3. Consolidate the RTT measurement logic.
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Signed-off-by: David S. Miller <davem@davemloft.net>