gluon-mesh-batman-adv-core: dont' call 'ip' to check if primary0 exists

package/gluon-mesh-batman-adv-core/luasrc/lib/gluon/mesh-batman-adv-core/config_mesh_interface

@@ -15,7 +15,7 @@ if cmd == 'setup' then
 
 	local mtu = tonumber(arg[2])
 
-	if os.execute('ip link show primary0 >/dev/null 2>&1') ~= 0 then
+	if not fs.access('/sys/class/net/primary0') then
 		os.execute([[
 			ip link add primary0 type dummy
 			echo 1 > /proc/sys/net/ipv6/conf/primary0/disable_ipv6