fusefs: diff reduction in fuse_kernel.h
Synchronize formatting and documentation in fuse_kernel.h with upstream
sources.
MFC after: 2 weeks
fusefs: implement FUSE_NO_OPEN_SUPPORT and FUSE_NO_OPENDIR_SUPPORT
For file systems that allow it, fusefs will skip FUSE_OPEN,
FUSE_RELEASE, FUSE_OPENDIR, and FUSE_RELEASEDIR operations, a minor
optimization.
MFC after: 2 weeks