Update hosts-and-services.md (#803)

If you check the code:
```
if instance.Spec.Network.DisableDefaultAllowedHosts {
				allowedHosts = make([]string, 0)
			}
```
Setting this to _true_ is what disables these hosts. the default was already false.

Author: ptnapoleon

docs/network_disruption/hosts-and-services.md

@@ -125,7 +125,7 @@ It can be configured easily [in the chart values.yaml file](../../chart/values.y
 
 ## Q: What are the default excluded hosts?
 
-These can be disabled by setting `network.disableDefaultAllowedHosts: false` in your Disruption's spec.
+These can be disabled by setting `network.disableDefaultAllowedHosts: true` in your Disruption's spec.
 
 ### Pod level network disruptions