SELinux: label created symlink instead of node

SELinux: label created symlink instead of node

The current code will label the target of a symlink rather than the
link itself.  This means that the link does not get it's context set
and the target gets the wrong context.
Incidentally this affects the labelling of hard disk device nodes and
can get in the way of booting.

Also get_media() should not be called with devname==NULL.