Set CONFIG_TUN=y in kernel config

This is needed by the PV ops kernel in order to support HVM guests with emulated VIFs

Signed-off-by: Alex Zeffertt <alex.zeffertt@xxxxxxxxxxxxx>

diff -r 11ca36cdd218 buildconfigs/enable-xen-config
--- a/buildconfigs/enable-xen-config	Mon Jun 14 19:00:25 2010 +0100
+++ b/buildconfigs/enable-xen-config	Mon Jun 14 19:02:07 2010 +0100
@@ -48,6 +48,7 @@
 setopt CONFIG_XEN_SYS_HYPERVISOR y
 setopt CONFIG_XEN_GNTDEV y
 setopt CONFIG_VMI y
+setopt CONFIG_TUN y
 
 setopt CONFIG_KVM y
 setopt CONFIG_KVM_INTEL y