If the transport had previously sent a RST_STREAM but had not yet
deleted the stream from its list of active streams, we should refund
connection-level flow control for any DATA frame received as such
DATA frames will never be read.

We already refund connection-level flow control if a stream closes with
unread data in bufPipe. However, when we receive a DATA frame after
reset, we don't bother writing it to bufPipe, so we have to refund the
flow control separately.

Updates golang/go#20469

Change-Id: I5a9810a5d6b1bd7e291173af53646246545a6665
Reviewed-on: https://go-review.googlesource.com/46591
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>