storm-control action.
none : no action will be taken.
block: packets will be blocked if receiving-rate is higher than the high water mark and will be unblocked only when the receiving-rate drops below the low water mark.
shutdown: the interface will be shutdown if receiving-rate is higher than the high water mark and the interface will NOT be open when the receiving-rate drops below the low water mark. To open the interface , use undo shutdown commond.