Revert is_unicast_global changes

Author: jstasiak

library/core/src/net/ip_addr.rs

@@ -1692,7 +1692,6 @@ impl Ipv6Addr {
     /// - unique local addresses
     /// - the unspecified address
     /// - the address range reserved for documentation
-    /// - 6to4 addresses
     ///
     /// This method returns [`true`] for site-local addresses as per [RFC 4291 section 2.5.7]
     ///
@@ -1726,8 +1725,6 @@ impl Ipv6Addr {
             && !self.is_unspecified()
             && !self.is_documentation()
             && !self.is_benchmarking()
-            // 6to4 (`2002::/16`), not documented as globally reachable by IANA
-            && self.segments()[0] != 0x2002
     }
 
     /// Returns the address's multicast scope if the address is multicast.

library/core/tests/net/ip_addr.rs

@@ -672,7 +672,7 @@ fn ipv6_properties() {
         global | unicast_global
     );
 
-    check!("2002::", &[0x20, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]);
+    check!("2002::", &[0x20, 0x02, 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);