Hi guys, sorry for late reply, I completely reinstalled Slackware (current, as Didier suggested) in order to exclude any possible wrong manipulation on my part (I haven't done, however, to be sure...), the 3.18.3 installation was new so no problems to start over.
Now wifi card goes well, bluetooth also, there is only a little problem with brightness setting that doesn't work, but I will solve it in my next free time.

I don't know how was happended, I recompiled 3.18.3 as is without any modification, buh...

Thanks to all for the support!