xen: set default timeout to 1 day rather than 1000 days

Unfortunately 1000 days is considered to be 'too long' by xen
(1000 days > 2^50 ns) which triggers a Linux bug workaround.
This causes the timer to be set to 100ms and a debug line printed
to the xen console.

Original-patch-by: Dimosthenis Pediaditakis <dimosthenis.pediaditakis@cl.cam.ac.uk>
Signed-off-by: David Scott <dave.scott@eu.citrix.com>