Some qdisc like htb want the parse_qopt to be called even if no options
present. Fixes regression caused by:

e9e78b0d is the first bad commit
commit e9e78b0d
Author: Stephen Hemminger <stephen@networkplumber.org>
Date:   Mon Aug 26 08:41:19 2013 -0700

    tc: allow qdisc without options