vlib: extend telnet protocol guard
vlib: extend telnet protocol guard

There is a number of TERMs with big length, such as
'screen.konsole-256color' (23). These TERMs can not
be processed properly by vpp because maximum telnet
byte stream supported is 24 and we need 6 more service
bytes to send TTYPE.

So I extended maximum depth guard to 32.

Type: fix
Signed-off-by: Vladimir Isaev <5c081b5db042874e7951a06bd180a0c41db4efef@netgate.com>
Change-Id: I9ca506996a97e9567d06483c5f020d6cc394329c

FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp