Linus named the upcoming 4.0 release of the kernel "Hurr Durr I'ma Sheep" (see his git commit), so we are celebrating this April Fool's day with a minor prank. If you've been redirected to imasheep.hurrdurr.org, do not panic. It's all part of the joke.
We've also restored all FTP and Rsync access to the mirrors.kernel.org servers, as we seem to have resolved our SSD and dm_cache problems. If you're still using FTP, however, please consider switching to HTTP. FTP is a protocol designed for a different era -- these days everyone should be avoiding it for multiple reasons.