security_dac: honor relabel='no' in chardev config
    
    The DAC driver ignores the relabel='no' attribute in chardev config
    
      <serial type='file'>
        <source path='/tmp/jim/test.file'>
          <seclabel model='dac' relabel='no'/>
        </source>
        <target port='0'/>
      </serial>
    
    This patch avoids labeling chardevs when relabel='no' is specified.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
    Signed-off-by: Jim Fehlig <jfehlig@suse.com>