Make sure all functions which use the convention that XXX_free(NULL)
is a nop are all documented.
The wording is chosen to match the documentation of free(3).
"If ptr is NULL, no operation is performed."
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Chengwen Feng <fengchengwen@huawei.com>
[David: squashed with other series updates, unified wording]
448e01f1b5