interfaces: evidence suggests + 2 is better than + 1 #7400

The + 1 was completely arbitrary to begin with (derived from
FreeBSD scripting), but if part of the system needs longer to
cope with tentative state then this would be an easy way to
make it more reliable.

If + 3 makes sense for the next person is something I want to
doubt, however.

Special thanks go to @Wireheadbe for pursuing and testing this.

src/etc/rc.newwanipv6

@@ -72,7 +72,7 @@ if (!$fp || !flock($fp, LOCK_EX | LOCK_NB)) {
 $dad_delay = (int)get_single_sysctl('net.inet6.ip6.dad_count');
 if ($dad_delay) {
     /* XXX this is also required but missed for IPv6 VIPs created later in the script */
-    sleep($dad_delay + 1);
+    sleep($dad_delay + 2);
 }
 
 /* this may be required to cleanse the DNS information no longer available */