net: annotate data-races around sk->sk_{data_ready,write_space}

In the Linux kernel, the following vulnerability has been resolved: net: annotate data-races around sk->sk_{data_ready,write_space} skmsg (and probably other layers) are changing these pointers while other cpus might read them concurrently. Add corresponding READ_ONCE()/WRITE_ONCE() annotations for UDP, TCP and AF_UNIX.