It looks to me like he's doing a split-S: rolling inverted into a half-loop. I doubt if eagles are capable of sustained negative-G flight - the wing muscle development would be all wrong, and the extreme camber of the wings wouldn't help. Nice photo though.
Edit: A nice photo of a Red Kite doing an impression of a Stuka -
http://www.flickr.com/photos/geoff-e/3925938345/