Implement SOCK_NONBLOCK flag to socket()
With the integration of 3666, the socket() implementation treats SOCK_NONBLOCK as a noop. This causes applications to believe the socket returned is in non-blocking more when it is not.
Implement the SOCK_NONBLOCK flag correctly. In addition, implement the SOCK_NDELAY flag to match accept4().
Return failure and set errno to EINVAL if unknown flags are passed in.