Revert "RDMA/ipoib: Fix warning caused by destroying non-initial netns"

This reverts commit 64f1fb6a which is
commit a3e74fb9247c ("RDMA/ipoib: Fix warning caused by destroying
non-initial netns") upstream.

It is not needed here as the netns_refund field is not present in this
tree anymore due to some reverts.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I0c1c729418ba0180cf27227e9b568a65b5e26942