desktop discovery: unmap IPv6 addresses (#31434)

We request only IPv4 addresses when doing DNS queries for Windows
desktops. In some circumstances, we can get addresses that are
represented ("mapped") as IPv6 addresses. Unmap them so that Teleport
always stores the IPv4 format.

lib/srv/desktop/discovery.go

@@ -208,8 +208,16 @@ func (s *WindowsService) lookupDesktop(ctx context.Context, hostname string) ([]
 					hostname, resolverName, err)
 			}
 
-			ch <- addrs
+			// even though we requested "ip4" it's possible to get IPv4
+			// addresses mapped to IPv6 addresses, so we unmap them here
+			result := make([]netip.Addr, 0, len(addrs))
+			for _, addr := range addrs {
+				if addr.Is4() || addr.Is4In6() {
+					result = append(result, addr.Unmap())
+				}
+			}
 
+			ch <- result
 		}()
 		return ch
 	}