net: annotate data-races around sk->sk_mark

[ Upstream commit 3c5b4d69 ]

sk->sk_mark is often read while another thread could change the value.

Fixes: 4a19ec58

 ("[NET]: Introducing socket mark socket option.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>