net/http: add StatusMisdirectedRequest (421)

Fixes #23776

Change-Id: Iff03d8b295afc1fd9435694b10246c723d323eda
Reviewed-on: https://go-review.googlesource.com/93296Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Kunpei Sakai <namusyaka@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/status.go

@@ -51,6 +51,7 @@ const (
 	StatusRequestedRangeNotSatisfiable = 416 // RFC 7233, 4.4
 	StatusExpectationFailed            = 417 // RFC 7231, 6.5.14
 	StatusTeapot                       = 418 // RFC 7168, 2.3.3
+	StatusMisdirectedRequest           = 421 // RFC 7540, 9.1.2
 	StatusUnprocessableEntity          = 422 // RFC 4918, 11.2
 	StatusLocked                       = 423 // RFC 4918, 11.3
 	StatusFailedDependency             = 424 // RFC 4918, 11.4
@@ -117,6 +118,7 @@ var statusText = map[int]string{
 	StatusRequestedRangeNotSatisfiable: "Requested Range Not Satisfiable",
 	StatusExpectationFailed:            "Expectation Failed",
 	StatusTeapot:                       "I'm a teapot",
+	StatusMisdirectedRequest:           "Misdirected Request",
 	StatusUnprocessableEntity:          "Unprocessable Entity",
 	StatusLocked:                       "Locked",
 	StatusFailedDependency:             "Failed Dependency",