xeniface: ignore freed context in EvtchnDpc()
xeniface: ignore freed context in EvtchnDpc()

omeg/xeniface,QubesOS/qubes-vmm-xen-win-pvdrivers-xeniface,QubesOS/qubes-vmm-xen-win-pvdrivers-xeniface,QubesOS/qubes-vmm-xen-win-pvdrivers-xeniface,omeg/xeniface,omeg/xeniface