Update libuweave/macaroon code

Added delegation time stamp into access token to match changed
validation logic of macaroons.

BUG: 26728665
Change-Id: I131b92b0e0b1b2274d80bdc0b5790a8c05071ec5
Reviewed-on: https://weave-review.googlesource.com/2467
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/third_party/libuweave/src/macaroon_caveat_internal.h b/third_party/libuweave/src/macaroon_caveat_internal.h
index 46a72fb..d6e7b07 100644
--- a/third_party/libuweave/src/macaroon_caveat_internal.h
+++ b/third_party/libuweave/src/macaroon_caveat_internal.h
@@ -20,8 +20,7 @@
                               size_t mac_tag_size);
 
 typedef struct {
-  bool has_issued_time;
-  uint32_t issued_time;
+  uint32_t issued_time;  // 0 when invalid or not set.
 } UwMacaroonValidationState;
 
 bool uw_macaroon_caveat_init_validation_state_(