udp: annotate data-race in __udp_enqueue_schedule_skb()

sk->sk_rcvbuf is read locklessly twice, while other threads
could change its value.

Use a READ_ONCE() to annotate the race.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240328144032.1864988-2-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>