libnetwork: fix TestParallel "bad file descriptor"
libnetwork: fix TestParallel "bad file descriptor"

When running inside a container, testns == origns. Consequently, closing
testns causes the deferred netns.Set(origns) call to fail. Stop closing
the aliased original namespace handle.

Signed-off-by: Cory Snider <2b734a4312be4b38906a3c89d31b95fd61f34b17@mirantis.com>

thaJeztah/docker,Ramzec/docker,trebonian/docker,thaJeztah/docker,Mokolea/docker,mahak/docker,moby/moby,moby/moby,moby/moby,jimjag/docker,konstruktoid/docker-upstream,Mokolea/docker,Mokolea/docker,Ramzec/docker,moby/moby,mahak/docker,jimjag/docker,trebonian/docker,konstruktoid/docker-upstream,thaJeztah/docker,trebonian/docker,konstruktoid/docker-upstream,mahak/docker,jimjag/docker,Ramzec/docker,thaJeztah/docker,Mokolea/docker,mahak/docker,trebonian/docker,konstruktoid/docker-upstream,jimjag/docker,Ramzec/docker