"[A] plan recordkeeper may receive sub-transfer agency fees to track participant-level ownership of shares. The DOL has recognized that such payments can improve efficiency and reduce the cost of administrative services. At the same time, the complexity of revenue sharing practices contributes to the need for the plan-level fee information required by recently effective regulations. Among other things, these regulations are intended to give plan sponsors the tools to oversee revenue sharing and ensure that plans do not pay excessive amounts for services as a result of such indirect payments."