Fix importing with symlinks

It turns out that symlinks are heavily used on Linux in /dev/disk.
So let's allow importing from them.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #12238