Read Payload after reading header in one call.

Increases performance, as it requires only minimum 1 call to read frame.
Before, at least 2 calls were required.

src/SerialMuxProtServer.hpp

@@ -400,14 +400,16 @@ class SerialMuxProtServer
      */
     void processRxData()
     {
-        uint8_t expectedBytes = 0;
-        uint8_t dlc           = 0;
+        uint8_t expectedBytes   = 0;
+        uint8_t dlc             = 0;
+        bool    expectingHeader = false;
 
         /* Determine how many bytes to read. */
         if (HEADER_LEN > m_receivedBytes)
         {
             /* Header must be read. */
-            expectedBytes = (HEADER_LEN - m_receivedBytes);
+            expectedBytes   = (HEADER_LEN - m_receivedBytes);
+            expectingHeader = true;
         }
         else
         {
@@ -431,6 +433,27 @@ class SerialMuxProtServer
                 m_receivedBytes += m_stream.readBytes(&m_receiveFrame.raw[m_receivedBytes], expectedBytes);
             }
 
+            if ((HEADER_LEN == m_receivedBytes) && (true == expectingHeader))
+            {
+                /* Header has been read. Get DLC of Rx Channel using Header. */
+                dlc = m_receiveFrame.fields.header.headerFields.m_dlc;
+
+                /* DLC = 0 means that the channel does not exist. */
+                if ((0U != dlc) && (MAX_RX_ATTEMPTS >= m_rxAttempts))
+                {
+                    expectedBytes = (dlc - (m_receivedBytes - HEADER_LEN));
+                    m_rxAttempts++;
+                }
+
+                if (0U != expectedBytes)
+                {
+                    if (expectedBytes <= m_stream.available())
+                    {
+                        m_receivedBytes += m_stream.readBytes(&m_receiveFrame.raw[m_receivedBytes], expectedBytes);
+                    }
+                }
+            }
+
             /* Frame has been received. */
             if ((0U != dlc) && ((HEADER_LEN + dlc) == m_receivedBytes))
             {