Log Message:
Add Xen 4.11.0 packages.
Note that there is a bug in 4.11 (also present in recent 4.6 and 4.8)
which causes an infrequent assert failure when running NetBSD PV guests.
The root cause has not been found, but a workaround is inclued which doesn't
seems to have ill effects. See xenkernel411/patches/patch-zz-bouyer
for details.