net: add test that TCP Close unblocks blocked Reads

net: add test that TCP Close unblocks blocked Reads

I guess this was fixed at some point. Remove a skipped test in
net/http and add an explicit test in net.

Fixes #17695

Change-Id: Idb9f3e236b726bb45098474b830c95c1fce57529
Reviewed-on: https://go-review.googlesource.com/33242
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>