Rollup merge of rust-lang#135745 - bardiharborow:std/net/rfc9602, r=cuviper

Recognise new IPv6 non-global range from IETF RFC 9602

This PR adds the `5f00::/16` range defined by [IETF RFC 9602](https://datatracker.ietf.org/doc/rfc9602/) to those ranges which `Ipv6Addr::is_global` recognises as a non-global IP. This range is used for Segment Routing (SRv6) SIDs.

See also: https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml
Unstable tracking issue: rust-lang#27709

Author: matthiaskrgr

library/core/src/net/ip_addr.rs

@@ -1623,6 +1623,8 @@ impl Ipv6Addr {
             // IANA says N/A.
             || matches!(self.segments(), [0x2002, _, _, _, _, _, _, _])
             || self.is_documentation()
+            // Segment Routing (SRv6) SIDs (`5f00::/16`)
+            || matches!(self.segments(), [0x5f00, ..])
             || self.is_unique_local()
             || self.is_unicast_link_local())
     }

library/coretests/tests/net/ip_addr.rs

@@ -689,6 +689,8 @@ fn ipv6_properties() {
 
     check!("2002::", &[0x20, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unicast_global);
 
+    check!("5f00::", &[0x5f, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unicast_global);
+
     check!("fc00::", &[0xfc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unique_local);
 
     check!(