icmppingsec values are in seconds instead of milliseconds

in 1.6 and before, values of icmppingsec items are stored in the database in seconds : 0.0015 means 1.5 millisecond
after upgrading to 1.8, icmppingsec item values are in milliseconds : 1.500 means 1.5 millisecond
but the GUI shows 1.5 seconds