net: Convert ovs_net_ops

net: Convert ovs_net_ops

These pernet_operations initialize and destroy net_generic()
data pointed by ovs_net_id. Exit method destroys vports from
alive net to exiting net. Since they are only pernet_operations
interested in this data, and exit method is executed under
exclusive global lock (ovs_mutex), they are safe to be executed
in parallel.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>