ANNAPOLIS, Md. -- An advertisement airing statewide urges Gov. Robert L. Ehrlich to veto a bill to study ways of making it easier for undocumented workers to obtain driver's licenses.A father who lost his son in the Sept. 11 attack on the World Trade Center recorded the radio spot for a group called 9/11 Families for a Secure America. It was paid for by the Federation for American Immigration Reform, a Washington-based group."He was 23 when terrorists struck the World Trade Center," Peter Gadiel of Connecticut says in the ad. "I can't bring Jamie back. But I can help...