[NETNS]: Consolidate kernel netlink socket destruction.
Denis V. Lunev authored

Create a specific helper for netlink kernel socket disposal. This just
let the code look better and provides a ground for proper disposal
inside a namespace.
Signed-off-by: default avatarDenis V. Lunev <den@openvz.org>
Tested-by: default avatarAlexey Dobriyan <adobriyan@openvz.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
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