The use_namespaces option has been defined as a workaround to kernels
not properly supporting namespaces. This limitation is behind us, it's
time to remove use_namespaces after its deprecation in Kilo in order to
simplify code and remove a poorly tested case (use_namespaces=False).
This change prepares for removal pullup_route method[1] which was only
used when use_namespaces=False.
[1] neutron.agent.linux.ip_lib
DocImpact
UpgradeImpact
Closes-Bug: #1508188
Related-Bug: #1435382
Depends-On: I303038eec560a6d99421140c2822aed8b518470b
Depends-On: I4feb2a15c7e1e4bfdbed2531b18b8e7d798ab3cc
Change-Id: I2fbf65df1250d9f9f1656b3964ee3b6de1ef1118
23b907bc6e