http/httpproxy: godoc fixes

Doc improvements:
- use godoc link to net/http
- link use go.dev instead of golang.org
- fix typo in ProxyFunc doc

Change-Id: I7be0ebc78b3c34bc50fac6edc2c20a713478a315
Reviewed-on: https://go-review.googlesource.com/c/net/+/757980
Auto-Submit: Nicholas Husin <nsh@golang.org>
Reviewed-by: Nicholas Husin <nsh@golang.org>
Reviewed-by: Nicholas Husin <husin@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

http/httpproxy/proxy.go

@@ -3,8 +3,8 @@
 // license that can be found in the LICENSE file.
 
 // Package httpproxy provides support for HTTP proxy determination
-// based on environment variables, as provided by net/http's
-// ProxyFromEnvironment function.
+// based on environment variables, as provided by
+// [net/http.ProxyFromEnvironment] function.
 //
 // The API is not subject to the Go 1 compatibility promise and may change at
 // any time.
@@ -56,7 +56,7 @@ type Config struct {
 	// presence of a REQUEST_METHOD environment variable).
 	// When this is set, ProxyForURL will return an error
 	// when HTTPProxy applies, because a client could be
-	// setting HTTP_PROXY maliciously. See https://golang.org/s/cgihttpproxy.
+	// setting HTTP_PROXY maliciously. See https://go.dev/s/cgihttpproxy.
 	CGI bool
 }
 
@@ -113,7 +113,7 @@ func getEnvAny(names ...string) string {
 // environment, or a proxy should not be used for the given request, as
 // defined by NO_PROXY.
 //
-// As a special case, if req.URL.Host is "localhost" or a loopback address
+// As a special case, if reqURL.Host is "localhost" or a loopback address
 // (with or without a port number), then a nil URL and nil error will be returned.
 func (cfg *Config) ProxyFunc() func(reqURL *url.URL) (*url.URL, error) {
 	// Preprocess the Config settings for more efficient evaluation.