Fix Telnet option processing issue

- A check for the length of the buffer should have used the provided
  'len' variable, not 'vec_len' since the buffer pointer may be
  within a vector, but not the start of one. 'vec_len' reports 0
  in that case, causing premature exit from the options processing
  loop and a wait for further input before it checks the next option.
- Also add TCP_NODELAY to CLI sockets to disable Nagle on TCP
  connections for a possible improvement in interactive response.

Change-Id: Ie1f53c003ca7d66bed51f437d298183215bad38c
Signed-off-by: Chris Luke <chrisy@flirble.org>