Revert "cmd/tailscale: access QNAP via localhost"

When running `tailscale web` as a standalone process,
it was necessary to send auth requests to QTS using
localhost to avoid hitting the proxy recursively.

However running `tailscale web` as a process means it is
consuming RAM all the time even when it isn't actively
doing anything.

After switching back to the `tailscale web` CGI mode, we
don't need to specifically use localhost for QNAP auth.

This reverts commit e0cadc5496.

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

cmd/tailscale/cli/web.go

@@ -223,8 +223,8 @@ func qnapAuthnQtoken(r *http.Request, user, token string) (string, *qnapAuthResp
 		"user":   []string{user},
 	}
 	u := url.URL{
-		Scheme:   "http",
-		Host:     "127.0.0.1:8080",
+		Scheme:   r.URL.Scheme,
+		Host:     r.URL.Host,
 		Path:     "/cgi-bin/authLogin.cgi",
 		RawQuery: query.Encode(),
 	}
@@ -237,8 +237,8 @@ func qnapAuthnSid(r *http.Request, user, sid string) (string, *qnapAuthResponse,
 		"sid": []string{sid},
 	}
 	u := url.URL{
-		Scheme:   "http",
-		Host:     "127.0.0.1:8080",
+		Scheme:   r.URL.Scheme,
+		Host:     r.URL.Host,
 		Path:     "/cgi-bin/authLogin.cgi",
 		RawQuery: query.Encode(),
 	}