ping: annotate data-races in ping_lookup()

isk->inet_num, isk->inet_rcv_saddr and sk->sk_bound_dev_if
are read locklessly in ping_lookup().

Add READ_ONCE()/WRITE_ONCE() annotations.

The race on isk->inet_rcv_saddr is probably coming from IPv6 support,
but does not deserve a specific backport.

Fixes: dbca1596bbb0 ("ping: convert to RCU lookups, get rid of rwlock")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260216100149.3319315-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>