i have found a solution, more like a workaround really but it helps to
add context to the problem.
i changed the wifi card from an atheros AR9462 to an atheros AR9485 that
showed the same type of behaviour: packet dropping , connection
reconnect to the ap, exactly the same pattern of regression but when i
was checking the dmesg log
it showed something about irq been remapped and reconnection occour.
[ 2364.308768] ath: phy0: DMA failed to stop in 10 ms AR_CR=0x00000028
i google it and found a workaround here :
i added the "intel_iommu=off" to the kernel at boot and everything
worked like a charm.
so just out of curiosity i switched back to the atheros AR9462 and tried
the same and it worked too.
so this is it.