dccp: annotate data-races in dccp_poll()

[ Upstream commit cba3f178 ]

We changed tcp_poll() over time, bug never updated dccp.

Note that we also could remove dccp instead of maintaining it.

Fixes: 7c657876

 ("[DCCP]: Initial implementation")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230818015820.2701595-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>