neighbour: Annotate access to neigh_parms fields.

neighbour: Annotate access to neigh_parms fields.

NEIGH_VAR() is read locklessly in the fast path, and IPv6 ndisc uses
NEIGH_VAR_SET() locklessly.

The next patch will convert neightbl_dump_info() to RCU.

Let's annotate accesses to neigh_param with READ_ONCE() and WRITE_ONCE().

Note that ndisc_ifinfo_sysctl_change() uses &NEIGH_VAR() and we cannot
use '&' with READ_ONCE(), so NEIGH_VAR_PTR() is introduced.

Note also that NEIGH_VAR_INIT() does not need WRITE_ONCE() as it is before
parms is published.  Also, the only user hippi_neigh_setup_dev() is no
longer called since commit e3804cbebb67 ("net: remove COMPAT_NET_DEV_OPS"),
which looks wrong, but probably no one uses HIPPI and RoadRunner.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251022054004.2514876-3-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>