Return the length of the `id` field,
    according to its real encoded type

def _ldp_id_adjustlen(pkt, x):
    """Return the length of the `id` field,
    according to its real encoded type"""
    f, v = pkt.getfield_and_val('id')
    return len(_LLDPidField.i2m(f, pkt, v)) + 1