Dell founder Michael Dell, left, in a Jan. 26, 2011 file photo, and Carl Icahn, in an Oct. 7, 2007 file photo, are seen in a combination photo. Dell’s largest independent shareholder has teamed with activist investor Icahn in another challenge to Michael Dell’s $24.4 billion bid to take the struggling computer maker private. Southeastern Asset Management and Icahn said in a letter sent on Thursday to the Dell Inc. board that they want to let shareholders keep their stock and give them either $12 per share in cash or additional shares in a deal that keeps the company publicly traded. An investment group led by Michael Dell offered earlier this year to pay $13.65 per share in a deal that would take the company private. Southeastern and Icahn criticized that proposal in a scathing letter to Dell’s board outlining their latest offer.