Poor guest network performance when using ixgbe with RSC enabled

Issue

• Poor guest network performance between a guest hosted on RHEL 6 KVM or RHEV3 and another system when using an Intel 10Gb/s NIC that uses the ixgbe module if vlan is used.
• It doesn't matter whether the guest uses the virtio network card or e1000.
• The network card that uses ixgbe driver is "08:00.0 Ethernet controller: Intel Corporation 82599EB 10 Gigabit Dual Port Backplane Connection (rev 01)"