Apply suggestions from code review

Co-authored-by: Boris Zbarsky <bzbarsky@apple.com>

Author: pidarped

src/app/ReadHandler.cpp

@@ -921,11 +921,11 @@ void ReadHandler::ClearStateFlag(ReadHandlerFlags aFlag)
 
 size_t ReadHandler::GetReportBufferMaxSize()
 {
-    size_t maxBufSize                  = chip::app::kMaxSecureSduLengthBytes;
+    size_t maxBufSize                  = kMaxSecureSduLengthBytes;
     Transport::SecureSession * session = GetSession();
     if (session && session->AllowsLargePayload())
     {
-        maxBufSize = chip::app::kMaxLargeSecureSduLengthBytes;
+        maxBufSize = kMaxLargeSecureSduLengthBytes;
     }
 
     return maxBufSize;

src/app/ReadHandler.h

@@ -335,9 +335,10 @@ class ReadHandler : public Messaging::ExchangeDelegate
 
     /*
      * Get the appropriate size of a packet buffer to allocate for encoding a Report message.
-     * Depending on the underlying session, which may or may not support large
-     * payloads, a buffer with the corresponding max size would be allocated.
+     * This size might depend on the underlying session used by the ReadHandler.
      *
+     * The size returned here is the size not including the various prepended headers
+     * (what System::PacketBuffer calls the "available size").
      */
     size_t GetReportBufferMaxSize();