neighbour: Use RCU list helpers for neigh_parms.list writers.

neighbour: Use RCU list helpers for neigh_parms.list writers.

We will convert RTM_GETNEIGHTBL to RCU soon, where we traverse
tbl->parms_list under RCU in neightbl_dump_info().

Let's use RCU list helper for neigh_parms in neigh_parms_alloc()
and neigh_parms_release().

neigh_table_init() uses the plain list_add() for the default
neigh_parm that is embedded in the table and not yet published.

Note that neigh_parms_release() already uses call_rcu() to free
neigh_parms.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251022054004.2514876-2-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>