- Close inherited file descriptors

wide-dhcpv6 binaries should close inherited fds.

- Close file descriptors on exec

Avoid FD leakage to children.

--- dhcp6relay.c.orig	Sun Jun 15 03:48:41 2008
+++ dhcp6relay.c	Sun Jan 10 00:50:57 2016
@@ -207,8 +207,14 @@ main(argc, argv)
 	}
 
 	if (foreground == 0) {
+		int fd;
+
 		if (daemon(0, 0) < 0)
 			err(1, "daemon");
+
+		for (fd = 3; fd < 1024; fd++)
+			close(fd);
+
 		openlog(progname, LOG_NDELAY|LOG_PID, LOG_DAEMON);
 	}
 	setloglevel(debug);
@@ -353,6 +359,7 @@ relay6_init(int ifnum, char *iflist[])
 		    gai_strerror(error));
 		goto failexit;
 	}
+	res->ai_socktype |= SOCK_CLOEXEC;
 	csock = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
 	if (csock < 0) {
 		dprintf(LOG_ERR, FNAME, "socket(csock): %s", strerror(errno));
@@ -459,6 +466,7 @@ relay6_init(int ifnum, char *iflist[])
 		goto failexit;
 	}
 	memcpy(&sa6_client, res->ai_addr, sizeof (sa6_client));
+	res->ai_socktype |= SOCK_CLOEXEC;
 	ssock = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
 	if (ssock < 0) {
 		dprintf(LOG_ERR, FNAME, "socket(outsock): %s",