Merge branch 'pid-introduce-helper-task_is_in_root_ns'

Merge branch 'pid-introduce-helper-task_is_in_root_ns'

Leo Yan says:

====================
pid: Introduce helper task_is_in_root_ns()

This patch series introduces a helper function task_is_in_init_pid_ns()
to replace open code.  The two patches are extracted from the original
series [1] for network subsystem.

As a plan, we can firstly land this patch set into kernel 5.18; there
have 5 patches are left out from original series [1], as a next step,
I will resend them for appropriate linux-next merging.

[1] https://lore.kernel.org/lkml/20211208083320.472503-1-leo.yan@linaro.org/
====================

Link: https://lore.kernel.org/r/20220126050427.605628-1-leo.yan@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>