Add mntns filter support

[houstar]

Current situation
[ Please describe the current situation you would like to have improved ]
Currently bcc-tools supported filter by mntns and cgroup. so could we add mntns filter here to support the old kernel that
haven't cgroup-v2.

Impact
[ Please describe the impact the lack of the feature requested is creating ]

Ideal future situation
[ Please describe the future situation after the improvement was implemented ]

Implementation options
[ Optional: please provide one or more options for implementing the feature requested ]

Additional information
[ Please Add any information that does not fit into any of the above sections here ]