Added new '-netns' option to simplify executing following cmd:

    ip netns exec NETNS tc OPTIONS COMMAND OBJECT

    to

    tc -n[etns] NETNS OPTIONS COMMAND OBJECT

e.g.:

    tc -net vnet0 qdisc
Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>