No cmdlet for that, you'll have to use the API.
Something like this for example.
Note that the values need to be in Mbps
$vmName = 'MyVM'$nicName = 'Network adapter 1'
$limitGbps = 8
$reservationGbps = 2
$vm = Get-VM -Name $vmName
$nic = Get-NetworkAdapter -VM $vm -Name $nicName
$spec = New-Object VMware.Vim.VirtualMachineConfigSpec
$dev = New-Object VMware.Vim.VirtualDeviceConfigSpec
$dev.Operation = [VMware.Vim.VirtualDeviceConfigSpecOperation]::edit
$dev.Device = $nic.ExtensionData
$dev.Device.ResourceAllocation.Limit = $limitGbps * 1KB
$dev.Device.ResourceAllocation.Reservation = $reservationGbps * 1KB
$spec.DeviceChange += $dev
$vm.ExtensionData.ReconfigVM($spec)