This reverts commit 6d5afd1a6f.
Because Netlink solution moves privileged privsep process into netns
without moving it back to root netns which could break other methods
using privileged process in neutron.
A follow-up change will rethink Netlink solution to correct its netns
management and improves code documentation/coverage/safety.
This change doesn't revert requirements.txt. It will allow to backport
the revert of this change (ie: allow to backport the rethinked Netlink
solution).
Partial-Bug: #1664294
Change-Id: I0c2d3b90a5799ce8d3baf4d20e95b352d12dbdc7
01ae5e7ec0