Hi! I have been able to get the WiFi connected continuously to the AP for 112 hours and counting (almost five days!). Now the WiFi follows the AP frequency changes seamlessly without any drop.
What did I do? I removed the crda and wireless-regdb packages. I have been suspecting of them long time ago and after many experiments I discovered wireless-regdb is Debian was (is) terribly outdated, so I filled a bug ( https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=949553 ), and the bug was corrected some days later, at least on testing and unstable, because stable has still the outdated package. I installed the new version in stable, but drops still happened, so I decided to completely remove any wireless restriction/configuration removing wireless-regdb and crda. Now my system has a wireless regdomain 00: DFS-UNSET, which is a sort of lowest common denominator for all wireless regdoms... but now it works just fine. I have seen in syslog dozens and dozens of AP frequency changes and the system followed all of them without any single problem. Now it is cristal clear there is a big issue with WiFi in Debian. I don't know if the kernel does not understand the info contained in the wireless-regdb database, or the info in the wireless-regdb is just wrong. This will be the next step.
