Make Dot11EltVendorSpecific packet extensible (#4660)

* Make Dot11EltVendorSpecific packet extensible

See #4659

This commit allows the Dot11EltVendorSpecific packet to dispatch to its
subclasses based on their OUI, with the same idiom that the parent
Dot11Elt uses to select subclasses based on their ID already:

https://github.com/secdev/scapy/blob/c15a670926185f6ddb9b3330ed1f947ff6f14b92/scapy/layers/dot11.py#L1057-L1074

This is just a rough sketch, so feedback very welcome to make sure it is
heading in the right direction :)

* Fix copy-paste typo

* Fix child register_variant swallowing call to parent register_variant

* Fix 'TODO'

* Remove comment

---------

Co-authored-by: gpotter2 <10530980+gpotter2@users.noreply.github.com>

Author: Hoolean

scapy/layers/dot11.py

@@ -1439,22 +1439,25 @@ class Dot11EltVendorSpecific(Dot11Elt):
     def dispatch_hook(cls, _pkt=None, *args, **kargs):
         if _pkt:
             oui = struct.unpack("!I", b"\x00" + _pkt[2:5])[0]
-            if oui == 0x0050f2:  # Microsoft
-                type_ = orb(_pkt[5])
-                if type_ == 0x01:
-                    # MS WPA IE
-                    return Dot11EltMicrosoftWPA
-                elif type_ == 0x02:
-                    # MS WME IE TODO
-                    # return Dot11EltMicrosoftWME
-                    pass
-                elif type_ == 0x04:
-                    # MS WPS IE TODO
-                    # return Dot11EltWPS
-                    pass
-                return Dot11EltVendorSpecific
+            ouicls = cls.registered_ouis.get(oui, cls)
+            if ouicls.dispatch_hook != cls.dispatch_hook:
+                # Sub-classes can have their own dispatch_hook
+                return ouicls.dispatch_hook(_pkt=_pkt, *args, **kargs)
+            cls = ouicls
         return cls
 
+    registered_ouis = {}
+
+    @classmethod
+    def register_variant(cls):
+        oui = cls.oui.default
+        if not oui:
+            # This is Dot11EltVendorSpecific, register it in the super-class.
+            super().register_variant()
+        elif oui not in cls.registered_ouis:
+            # Sub-Vendor (e.g. Dot11EltMicrosoftWPA)
+            cls.registered_ouis[oui] = cls
+
 
 class Dot11EltMicrosoftWPA(Dot11EltVendorSpecific):
     name = "802.11 Microsoft WPA"
@@ -1467,6 +1470,24 @@ class Dot11EltMicrosoftWPA(Dot11EltVendorSpecific):
         XByteField("type", 0x01)
     ] + Dot11EltRSN.fields_desc[2:8]
 
+    @classmethod
+    def dispatch_hook(cls, _pkt=None, *args, **kargs):
+        if _pkt:
+            type_ = orb(_pkt[5])
+            if type_ == 0x01:
+                # MS WPA IE
+                return Dot11EltMicrosoftWPA
+            elif type_ == 0x02:
+                # MS WME IE TODO
+                # return Dot11EltMicrosoftWME
+                pass
+            elif type_ == 0x04:
+                # MS WPS IE TODO
+                # return Dot11EltWPS
+                pass
+            return Dot11EltVendorSpecific
+        return cls
+
 
 # 802.11-2016 9.4.2.19