Creates an X.25 protocol dte pvc entity which describes a
    permanent virtual circuit (PVC).

    create [node node-id] x25 protocol dte dte-name -
        pvc pvc-name -
        channel integer [,packet size integer] [,window size integer]

    The Channel argument is required.  It is the concatenated logical
    channel group and logical channel number for the PVC, and it
    should be a unique value among PVCs on this DTE.  These channel
    numbers must not be present in the incoming list or outgoing list
    of the parent DTE.

    Packet Size and Window Size are optional arguments.

    Example:

    create x25 protocol dte dte-0 pvc PVC-0 channel 5