Fix Sec-Fetch-Site header (#37277)

While working on #37209 I discovered that the header was computed
incorrectly. After carefully reading the specification, I realized that
the link in the spec was wrong and we were missing the fact that for
host-domains, we should operate on the registrable domain.

Additionally, the same-site call was missing the negation.

Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>

components/net/tests/http_loader.rs

@@ -329,7 +329,7 @@ fn test_request_and_response_data_with_network_messages() {
     );
     headers.insert(
         HeaderName::from_static("sec-fetch-site"),
-        HeaderValue::from_static("same-site"),
+        HeaderValue::from_static("cross-site"),
     );
     headers.insert(
         HeaderName::from_static("sec-fetch-user"),