munin-node-c: Fix input tokenizing (add "\r" to the delimiters)

* The telnet client is often used to connect a munin-node for debugging
  purpose. As telnet sends "\r\n" at the end of a line the output of the
  munin-node-c is wrong if only the "\n" is extracted from the input.
  With this patch the end-of-line is correct and telnet can be used to connect
  the munin-node-c when running in an inet-superserver.