proc: introduce proc_create_net_single

Variant of proc_create_data that directly take a seq_file show
callback and deals with network namespaces in ->open and ->release.
All callers of proc_create + single_open_net converted over, and
single_{open,release}_net are removed entirely.

Signed-off-by: Christoph Hellwig <hch@lst.de>
13 files changed