Too much engine oil! You've tipped in more engine oil than your motorcycle engine needs. It's not as bad as under-filling but too much oil in an motorcycle engine can cause a range of problems, the excess out of a breather pipe which can contaminate your air filter or make your tires dangerously slippery.
The solution's simple. Remove the excess. It's very difficult to do by taking out the oil drain bolt, so buy a big syringe instead. Fishing shops, pharmacies and chemists sell them and you can get really big ones from some shops (100ml or more). A bit of home brew tube or brake bleed pipe connected to the end should let you suck out the excess oil. Just don't do it when the engine's hot, plastic melts...and plastic pieces in the engine are a recipe for the need to split the engine.
The syringe should come in handy should you overfill a brake reservoir and also for measuring oil into fork legs. Clean the rubber bung to remove any oil before storing, as it can react and cause the whole thing to seize up.