do_linear: Linear duration-occupancy relation
In QinglongYan/ANSSI: Automated near-stationary state identifier

This function is applied to calculate the minimum acceptable duration given the occupancy based on a linear duration-occupancy relation

1	do_linear(occ, lot, hot, xhot, ldr, hdr, xhdr)

`occ`	Candidate occupancy, which is the input variable
`lot`	Low-occupancy threshold(*)
`hot`	High-occupancy threshold
`xhot`	Extremely high-occupancy threshold(*)
`ldr`	The minimum acceptable duration in low-occupancy periods(*)
`hdr`	The minimum acceptable duration in high-occupancy periods
`xhdr`	The minimum acceptable duration in extremely high-occupancy periods(*)