Borje Ekholm, the veteran executive brought in to turn around Swedish network-equipment maker Ericsson AB, faces tough decisions on staffing, competition and balance-sheet management that will test the former Investor AB chief’s ability to right the ship after a tumultuous 2016. Ekholm, a long-time board member at Stockholm-based Ericsson, takes over as chief executive officer on Monday at a company that saw its share price plummet 35 percent last year amid steep revenue declines, fierce competition from Chinese rivals, and dwindling carrier spending as large investments in fourth-generation wireless gear largely wound down.