@sunc,

It seems that your router does not properly support powersaving mode.
From your dmesg:
"wl1271: AP with dysfunctional ps-poll, trying to work around it."

That means the WLAN firmware detected that powersaving doesn't work OK with the router.

You could try disabling any power-saving options in your router (if at all possible) and/or disabling power-saving for WLAN on your N9 (no idea if that's possible, in the N900 it is).