[LTP] [PATCH] containers/netns: update netns shell test to new API

[Petr Vorel]

Hi Kory,

> Before merge I'll drop bogus '# TEST CASE #N' and add few TINFO messages, e.g.:
> tst_res TINFO "controlling device over netlink"
Thanks for your work, merged.
In the end without tst_res TINFO messages and added one cleanup commit.

I'm going to send a patch to ML which fixes tst_check_iproute check for recent
iproute2, which uses since v5.8.0 (actually since v5.7.0-77-gb687d1067169)
kernel version.

Kind regards,
Petr