hostinet/socket.go: the Sentry doesn't spawn new processes, but it doesn't hurt to protect the socket from leaking.
unet/unet.go: should be setting closing on exec. The FD is explicitly donated to children when needed.
PiperOrigin-RevId: 200135682
Change-Id: Ia8a45ced1e00a19420c8611b12e7a8ee770f89cb