model-wire: Fixing compliance with CCNb format regarding Content tag

Previously, content didn't contain a proper BLOB tag

Refs #1020 (http://redmine.named-data.net/issues/1020)
diff --git a/model/wire/ccnb/wire-ccnb-data.cc b/model/wire/ccnb/wire-ccnb-data.cc
index 0770c3d..e625e06 100644
--- a/model/wire/ccnb/wire-ccnb-data.cc
+++ b/model/wire/ccnb/wire-ccnb-data.cc
@@ -246,6 +246,10 @@
 
   Ccnb::AppendBlockHeader (start, CcnbParser::CCN_DTAG_Content, CcnbParser::CCN_DTAG); // <Content>
 
+  uint32_t payloadSize = m_data->GetPayload ()->GetSize ();
+  if (payloadSize > 0)
+    Ccnb::AppendBlockHeader (start, payloadSize, CcnbParser::CCN_BLOB);
+
   // there are no closing tags !!!
   // The closing tag is handled by ContentObjectTail
 }
@@ -319,6 +323,10 @@
 
   written += Ccnb::EstimateBlockHeader (CcnbParser::CCN_DTAG_Content); // <Content>
 
+  uint32_t payloadSize = m_data->GetPayload ()->GetSize ();
+  if (payloadSize > 0)
+    written += Ccnb::EstimateBlockHeader (payloadSize);
+
   // there are no closing tags !!!
   // The closing tag is handled by ContentObjectTail
   return written;