Add a conditional sleep 1 in case we add any IPv6 addresses to interfaces.

Do this per jail started, not per address.  This will allow DAD to complete
and services to properly start.   Before we have seen problems with services
trying to start before the IPv6 address was available to use and thus
erroring and failing to start.

MFC after:	3 days

etc/rc.d/jail

@@ -509,7 +509,7 @@ jail_handle_ips_option()
 		esac
 		case "${_type}" in
 		inet)	;;
-		inet6)	;;
+		inet6)	ipv6_address_count=$((ipv6_address_count + 1)) ;;
 		*)	warn "Could not determine address family.  Not going" \
 			    "to ${_action} address '${_addr}' for ${_jail}."
 			continue
@@ -546,6 +546,7 @@ jail_ips()
 	esac
 
 	# Handle addresses.
+	ipv6_address_count=0
 	jail_handle_ips_option ${_action} "${_ip}"
 	# Handle jail_xxx_ip_multi<N>
 	alias=0
@@ -558,6 +559,12 @@ jail_ips()
 			;;
 		esac
 	done
+	case ${ipv6_address_count} in
+	0)	;;
+	*)	# Sleep 1 second to let DAD complete before starting services.
+		sleep 1
+		;;
+	esac
 }
 
 jail_prestart()