VPP-27 Extend telnet protocol buffer guard

With Telnet protocol overhead, the string "xterm-256color", which is the
norm when the terminal is iTerm on a Mac, is longer than the 16 byte
lookahead overflow guard in the Telnet protocol processor.

This extends it to 24 bytes.

This guard is designed to encourage the protocol processor to quit
waiting for bytes indefinitely if those already in the buffer do not
form a complete message. Whilst this is unlikely, extending the guard
length would mean more bytes need to be received before it gives up.

Change-Id: Ibaa3d35b78bfd298fe0e4f4c6e508440f122e916
Signed-off-by: Chris Luke <chrisy@flirble.org>

vlib/vlib/unix/cli.c

@@ -71,7 +71,7 @@
 
 /** Maximum depth into a byte stream from which to compile a Telnet
  * protocol message. This is a saftey measure. */
-#define UNIX_CLI_MAX_DEPTH_TELNET 16
+#define UNIX_CLI_MAX_DEPTH_TELNET 24
 
 /** Unix standard in */
 #define UNIX_CLI_STDIN_FD 0