I suspect that when troll refers to dragging anything, it's just a spelling and regional pronunciation variant on trawl.
According to etymonline.com, the etymology of "trawl" is:
1560s, from Dutch tragelen, from Middle Dutch traghelen "to drag," from traghel "dragnet," probably from Latin tragula "dragnet." Related: Trawled; trawling.
Now, "troll" verb:
late 14c., "to go about, stroll," later (early 15c.) "roll from side to side, trundle," probably from Old French troller, a hunting term, "wander, to go in quest of game without purpose" (Modern French trôler), from a Germanic source (compare Old High German trollen "to walk with short steps"), from Proto-Germanic truzlanan.*
It's rather related to "stroll". Nothing in the semantics about fishing.
I suspect that "troll" in longline fishing in fact refers to the long line with many hooks being pulled around; i.e. "trawled".
