tcp: annotate data-races around tw->tw_ts_recent and tw->tw_ts_recent_stamp

These fields can be read and written locklessly, add annotations
around these minor races.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>