Socket file descriptors remain open across exec unless
SOCK_CLOEXEC is set. Enable this option, to avoid leaking
file descriptors.
In practice, this isn't a big deal, since the socket only remains
open for a very short period to write a message. However, this
socket might leak for for multithreaded programs if an exec occurs
between the open and close.
Change-Id: Ica2e71fe28657c32d56de1431c8f7f1f5c7b7c58
bae5b1dbd8