net/http/httputil: close hijacked connections when CloseWrite not available
CL 637939 changed ReverseProxy's handling of hijacked connections:
After copying all data in one direction, it half-closes the outbound
connection rather than fully closing both.
Revert to the old behavior when the outbound connection does not support
CloseWrite, avoiding a case where one side of the proxied connection closes
but the other remains open.
Fixes #72140
Change-Id: Ic0cacaa6323290f89ba48fd6cae737e86045a435
Reviewed-on: https://go-review.googlesource.com/c/go/+/655595 Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Damien Neil <dneil@google.com>