ext/sockets: adding Linux's TCP_USER_TIMEOUT constant.

[lucasnetau]

Useful to ensure PHP sockets are notified of socket failure when Sockets may be closed incorrectly and data can no longer be transmitted. eg Firewall dropping connection or peer device failure (commonly seen with Cloud load balancers).

From tcp(7) :It specifies the maximum amount of time in milliseconds that transmitted data may remain unacknowledged, or buffered data may remain untransmitted (due to zero window size) before TCP will forcibly close the corresponding connection and return ETIMEDOUT to the application.

Following #13816 for PR format for socket constants/

[devnexen]

my bad, I realise ov is an int.
you would need the following change

zend_long timeout = zval_get_long(arg4);
<overflow check on timeout>
unsigned int val = (unsigned int)timeout;
optlen = sizeof(val);
opt_ptr = &val;