Every trucking company in America was suddenly required by law to buy the thing Samsara happened to sell. a16z GP Andy McCall, who ran Samsara revenue through the IPO, tells the story: "Prior to 2016, truckers had these manual logbooks... You would write down in your logbook, 'I just drove for four hours, now I'm taking a 20-minute break.'" "Around 2016, they implemented this ELD mandate: electronic logging devices. Hey, we can use technology to actually track when the vehicle's moving and…