net/http: add link to types

net/http: add link to types

Some types are not linked.
This change adds a link to each type.

Change-Id: Id46fb64a74efb851ed76e4136f15e8fd9e445bb7
Reviewed-on: https://go-review.googlesource.com/c/go/+/663075
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>