[PATCH] sysctl: decnet: remove unnecessary insert_at_head flag

The sysctl numbers used are unique so setting the insert_at_head flag does not
succeed in overriding any sysctls, and is just confusing because it doesn't.
Clear the flag.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Patrick Caulfield <patrick@tykepenguin.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>