isgx: fix: clear flag for directory parameter in smackload/smackctl

Clear flag was not properly applied when directory is given
for smackload. This patch fixes the issue. I decided to move
into opendir/readdir approach because nftw() does not support
supplying any kind of state to the callback. The end result
looks also more manageable that we had before.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Merge remote-tracking branch 'jsakkine/issue64' into v1.0.x