[PATCH 1/2] RFC: sysctl: write ctl_table->extra2 to table entries created from a ctl_path

For each entry in an array of 'struct ctl_path' we were registering a
'struct ctl_table' array with two entries:
A) one to store the name + permissions,
B) one as an end-of-array marker (completely blank).

but we were not using any of the data storage fields
(data, extra1, extra2) in the first 'struct ctl_table'.

This adds possibility of storring some user provided
pointer in the 'extra2' field.

All users these functions store NULL in the 'extra2'
field like they used to before this patch:
* register_sysctl_paths
* register_net_sysctl_table
* register_net_sysctl_rotable

Until now sysctl_check_table considered that the 'struct ctl_table' of
directories may not store anything in the 'extra2' field. We no longer
consider this a fault.

Signed-off-by: Lucian Adrian Grijincu <redacted>
---
 include/linux/sysctl.h      |    2 +-
 include/net/net_namespace.h |    2 ++
 kernel/sysctl.c             |    7 +++++--
 kernel/sysctl_check.c       |    2 --
 net/sysctl_net.c            |   20 ++++++++++++++------
 5 files changed, 22 insertions(+), 11 deletions(-)