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 ]