You can use the MoveIntoFolder_Task method found on the folder object.
http://pubs.vmware.com/vsphere-55/index.jsp?topic=%2Fcom.vmware.wssdk.apiref.doc%2Fvim.Folder.html
If you have any port groups attached to the dvs they will also need to be moved as well. Here is a sample script that I wrote and tested with one dvs and two port groups. I am sure there is a more elegant approach but this should get the job done.
$folder = Get-Folder -Type Network -Name folderName | Get-View
$dvs = Get-VirtualSwitch -Name dvsName
$dvPGs = $dvs | Get-VirtualPortGroup
$count = $dvs.count + $dvPGs.count
$list = New-Object VMware.Vim.ManagedObjectReference[] ($count)
$list[0] = New-Object VMware.Vim.ManagedObjectReference
$list[0].type = $dvs.Extensiondata.MoRef.Type
$list[0].value = $dvs.Extensiondata.MoRef.Value
$dvPgCount = 1
foreach ($dvPg in $dvPgs) { $list[$dvPgCount] = New-Object VMware.Vim.ManagedObjectReference $list[$dvPgCount].type = $dvPg.Extensiondata.MoRef.Type $list[$dvPgCount].value = $dvPg.Extensiondata.MoRef.Value $dvPgCount++
}
$folder.MoveIntoFolder_Task($list)