Looks like you may have to use the Get-EsxCli cmdlet to get that information.
Here's what I would do. You already have your list of host and network adapters (I would also specify "-Physical" on Get-VMHostNetworkAdapters to eliminate the VMkernel adapters).
$nic_info = Get-VMHostNetworkAdapter -Physical | Select VMHost, Name
$nic_collection = @()
foreach ($nic in $nic_info)
{
$esxcli_cmd = Get-EsxCli -VMHost $nic.VMHost
$collect_info = "" | Select VMHost, vmnic, Description
$collect_info.VMHost = $nic.VMHost
$collect_info.vmnic = $nic.Name
$collect_info.Description = ($esxcli.network.nic.list() | where {$_.Name -match $nic.Name}).Description
$nic_collection += $collect_info
}
Write-Host $nic_collection