face/rib/tools: avoid deprecate Block::fromBuffer overloads

refs #2553

Change-Id: I32ea424ab7547f59fea2fca70ad6f41cd90bab58
diff --git a/daemon/face/ethernet-face.cpp b/daemon/face/ethernet-face.cpp
index 8bd2c7b..d2cd9a1 100644
--- a/daemon/face/ethernet-face.cpp
+++ b/daemon/face/ethernet-face.cpp
@@ -381,8 +381,9 @@
   length -= ethernet::HDR_LEN;
 
   /// \todo Reserve space in front and at the back of the underlying buffer
+  bool isOk = false;
   Block fragment;
-  bool isOk = Block::fromBuffer(packet, length, fragment);
+  std::tie(isOk, fragment) = Block::fromBuffer(packet, length);
   if (!isOk)
     {
       NFD_LOG_FACE_WARN("Block received from " << sourceAddress.toString()