Cisco said today it would up its offer to buy Tandberg to $3.4 billion — a boost of $400 million over its original bid, made last month — and said 40 percent of Tandberg’s shareholders have so far accepted the deal (Cisco needs 90 percent). About two weeks after the networking giant offered to buy the Norwegian video conferencing equipment maker, a group of shareholders protested, saying the offer was too low. This new offer should placate those shareholders, one of which was a brokerage firm that at the time of the original announcement had a target value on the shares that was slightly lower than the per-share price Cisco is now offering.