code: func IPv6(t *testing.T, b []byte, checkers ...NetworkChecker) {
  	t.Helper()
  
  	ipv6 := header.IPv6(b)
  	if !ipv6.IsValid(len(b)) {
  		t.Error("Not a valid IPv6 packet")
  	}
  
  	for _, f := range checkers {
  		f(t, []header.Network{ipv6})
  	}
  	if t.Failed() {
  		t.FailNow()
  	}
  }
docs: // IPv6 checks the validity and properties of the given IPv6 packet. The usage
  // is similar to IPv4.