Comment 16 for bug 1423631

I found the cause of the problem.
The tap interface of a instance has small tx length 500 packets. At a high network load (15-25 Kpps) and high CPU load on a guest some times queue overflows and the tap interface start drop network packages. I think that queue overflow occurs in moments of micro friezes (<1000ms) of a virtual machine. I solved this problem by increasing the tx_queue up to 10000.