[NET]: Make core networking code use seq_open_private

This concerns the ipv4 and ipv6 code mostly, but also the netlink
and unix sockets.

The netlink code is an example of how to use the __seq_open_private()
call - it saves the net namespace on this private.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
15 files changed