CP-38020: enable best effort NUMA affinity placement by default

For some workloads this is an improvement: it places VMs on a small number of NUMA node,
so each VM will perform local memory accesses where possible, which has lower latency.

There are some workloads where this is a regression: now a VM can only use the bandwidth of a single
NUMA node, rather than all NUMA nodes. However this advantage is only present while the VM is the only one using the system,
if there are multiple VMs then fairly soon they will all do remote memory accesses, overloading the QPI links.

The user can still override this on a host by host basis if their workloads require the previous behaviour.

TODO: some actual benchmarks to support this theory

Signed-off-by: Edwin Török <[email protected]>

ocaml/xapi/xapi_xenops.ml

@@ -3146,7 +3146,7 @@ let set_numa_affinity_policy ~__context ~value =
     | `best_effort ->
         Best_effort
     | `default_policy ->
-        Any
+        Best_effort
   in
   Client.HOST.set_numa_affinity_policy dbg value