luci-base: drop ipv6 lease status when IPV6 is not support

Signed-off-by: Rosy Song <rosysong@rosinson.com>

modules/luci-base/luasrc/view/lease_status.htm

@@ -79,6 +79,12 @@
 	</div>
 </div>
 
+<%
+	local fs = require "nixio.fs"
+	local has_ipv6 = fs.access("/proc/net/ipv6_route")
+
+	if has_ipv6 then
+-%>
 	<div class="cbi-section" style="display:none">
 		<h3><%:Active DHCPv6 Leases%></h3>
 		<div class="table" id="lease6_status_table">
@@ -93,3 +99,4 @@
 			</div>
 		</div>
 	</div>
+<% end -%>