xsm: dummy module - implement missing stub

- This minor patch implements the missing stub function
security_label_to_details in the dummy module.  This stub function is
necessary to create domains with network interfaces for modules that
do not implement the security_label_to_details function.

Signed-off-by: George Coker <gscoker@alpha.ncsc.mil>

tools/python/xen/util/xsm/dummy/dummy.py

@@ -131,3 +131,6 @@ def dump_policy_file():
 
 def get_ssid(domain):
     err("No ssid has been assigned to any domain under xsm dummy module.")
+
+def security_label_to_details(res_label):
+    return ("","","")