Answer a firmware category request over ipmi honestly

nodefirmware <node> disks reported the bmc version, and so did adapters and
misc. The generic handler takes a category and ignores it, and the ipmi plugin
does not filter either, so every category answered with the one entry ipmi can
report.

Apply the rule R13 established for a redfish inventory that does not categorise
itself: the bmc's own firmware is system firmware, so it answers for core and
for nothing else. Filtering in the handler that produces the entry leaves an oem
handler that does categorise its own firmware free to answer for more.

confluent_server/aiohmi/ipmi/oem/generic.py

@@ -301,6 +301,11 @@ class OEMHandler(object):
         # code to know whether it cares or not.  The main purpose of the
         # components argument is to indicate when certain performance
         # optimizations can be performed.
+        if category not in (None, 'all', 'core'):
+            # The bmc firmware is system firmware, so it is the answer to
+            # 'core' and to nothing else. Without this a request for, say,
+            # disk firmware answers with the bmc version.
+            return
         yield 'BMC Version', {'version': bmcver}
 
     async def get_oem_capping_enabled(self):