Default vfs.fastdev to 1 for wider testing, so the vnode bypass for device

Default vfs.fastdev to 1 for wider testing, so the vnode bypass for device
read and write is now the default.

This is a precursor to the continued work on a kernel-managed cache layer
on top of the VFS layer.  That is, the intention is to eventually switch the
VM page cache to be ABOVE the VFS layer rather then BELOW the VFS layer for
standard read() and write() calls, with potentially major performance
benefits.