netns: avoid disabling irq for netns id

Bring back commit bc51dddf ("netns: avoid disabling irq for netns
id") now that we've fixed some audit multicast issues that caused
problems with original attempt.  Additional information, and history,
can be found in the links below:

 * https://github.com/linux-audit/audit-kernel/issues/22
 * https://github.com/linux-audit/audit-kernel/issues/23



Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>