Use kern_ioctl() rather than ioctl() for testing the FBT provider, since the
latter doesn't exist in FreeBSD. All the tests under fbtprovider pass now.
Detect unsupported PREVENT ALLOW MEDIUM REMOVAL and SYNCHRONIZE CACHE(10)
to not spam devices with useless commands and logs with errors.
Oops, revert unwanted part of r253721.
Provide some examples for watchdogd usage.