Here is the script I use
$vh01=$hostname6
$vh01moref=$vh01 | % {get-view $_.Id}
$vh01morefconfig=$vh01moref.configmanager
$vh01netsys=$vh01morefconfig.networksystem
$vh01netsysmoref=get-view $vh01netsys
foreach ($vh01vsw0 in $vh01netsysmoref.NetworkConfig.Vswitch){
$swspec= $vh01vsw0.Spec
$swspec.policy.security.allowPromiscuous=$false
$swspec.policy.security.forgedTransmits=$true
$swspec.policy.security.macChanges=$false
$vh01netsysmoref.UpdateVirtualSwitch($vh01vsw0.name,$swspec)
}