The current ns package code is very careful about not leaving the calling
thread with the overridden namespace set, for example when origns.Set() fails.
This is achieved by starting a new green thread, locking its OS thread, and
never unlocking it. Which makes golang runtime to scrap the OS thread backing
the green thread after the go routine exits.
While this works, it's probably not as optimal: stopping and starting a new OS
thread is expensive and may be avoided if we unlock the thread after resetting
network namespace to the original. On the other hand, if resetting fails, it's
better to leave the thread locked and die.
While it won't work in all cases, we can still make an attempt to reuse the OS
thread when resetting the namespace succeeds. This can be achieved by unlocking
the thread conditionally to the namespace reset success.
Signed-off-by: Ihar Hrachyshka <ihrachys@redhat.com>
Namespace creation had an unergonomic interface and isn't used, except
for testing code. Remove it; downstream users should really be creating
their own namespaces
- start list of linux_only plugins; ignore them when testing on Windows
- Isolate linux-only code by filename suffix
- Remove stub (NotImplemented) functions
- other misc. fixes for Windows compatibility
