Do not listen unless configured with cli-listen.

Do not listen unless configured with cli-listen.

I noticed while mucking about with lsof that vpp
was listening on port 5000.

telnet 0 5000 revealed that it was listening for
the cli on that port.

Digging into the code, it turns out that if you
do not configure cli-listen (Example:

unix {
     cli-listen localhost:5002
}
)

Then vpp is listening on the first available port
starting at port 5000 anyway.  This is a simple
patch to *not* listen unless configured to do so.

Change-Id: Id7f6f4d69e0a1642d2767849a90b21f38f21ecaa
Signed-off-by: Ed Warnicke <[email protected]>