vif segment fault with -list arg

[Robert Ellis]

VIF has a segmentation fault with the current master branch on ubuntu 14.04.4 when a -list is passed as the argument instead of --list. It should display the help out instead.

Example:
stack@ubuntu:/usr/bin$ vif -list
Segmentation fault (core dumped)

This has been reproduced on the 3.0 contrail release as well.

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/21081
Submitter: Robert Ellis (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/21081
Committed: http://github.org/Juniper/contrail-vrouter/commit/54cf539e8da7a8129b03dd4302de8188df017563
Submitter: Zuul
Branch: master

commit 54cf539e8da7a8129b03dd4302de8188df017563
Author: Robert Ellis <email address hidden>
Date: Fri Jun 10 10:41:45 2016 -0500

Fixes vif vRouter segment fault with bad arguments

When vif is used with some invalid combinations of arguments it will
core dump with a segmentation fault. For example if vif -list is done
a core dump will happen. This is due to calling strtoul with a NULL
string. Adding a new procedure that will check if the string is NULL.

Change-Id: I5015c07e76a4434498229862f5172c2802ae99e9
Closes-Bug: #1590964