Nelly was arrested for possession of four ecstasy pills during a late-night gambling spree in a casino. RadarOnline.com can confirm the 49-year-old rapper, born Cornell Haynes II, was at the Hollywood Casino in St. Charles, Missouri, when a police officer ran a background check on him, leading to his arrest. Online police records show the Grammy-winning artist — who is expecting his first child with wife Ashanti, 43 — was charged with possession of a controlled substance. He was booked at 4:45 a.m. Wednesday morning and later released the same day. In a statement provided to Page Six, the Miss…