dup2 and setsockopt can use the lock in conn to protect resources,
the lock in accept is originally used to protect the connection status.
however, only the send, recv, netpoll, and connect processes will
check this flag. only when the interface returns will the corresponding
conn structure be exposed to the caller, and then the above operations
can be performed. Therefore, this net_lock is not necessary.
Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>