Fix inverse sleep logic in buf_daemon().
Before commit 3cec5c77 buf_daemon() went to longer 1s sleep if numdirtybuffers <= lodirtybuffers. After that commit new condition !BIT_EMPTY(BUF_DOMAINS, &bdlodirty) got opposite -- true when one or more more domains is above lodirtybuffers. As result, on freshly booted system with no dirty buffers buf_daemon() wakes up 10 times per second and probably only 1 time per second when there is actual work to do. MFC after: 1 week Reviewed by: kib, markj Tested by: pho Differential revision: https://reviews.freebsd.org/D33890 (cherry picked from commit e76c0108)