Defense IT specialist Leidos Holdings (LDOS -5.59%) beat quarterly expectations, but investors apparently were hoping for more. Leidos shares fell 7% at market open Tuesday and were down 5% as of 11 a.m. ET.Margin softness in an otherwise strong quarterLeidos is the largest of the so-called "Beltway Bandits" -- defense companies that provide IT and other services to military, intelligence, and civilian agencies. The company earned $2.37 per share in the fourth quarter on revenue of $4.4 billion, surpassing ...