Improve CDPMsgIPPrefix : allow more than one IP address (#4585)

* Update cdp.py for CDPIPPrefix

if the length of IP addresses prefixes was more than one address all the following content wasn't interpreted (Raw payload). This seams to fix it

* Update cdp.py

A better approach with a list rather than packets

* Update cdp.py case error on Prefix

* Fix PEP8 formatting

* Rename IPPrefix -> CDPPrefix

---------

Co-authored-by: gpotter2 <[email protected]>

Author: itform-fr

scapy/contrib/cdp.py

@@ -250,13 +250,23 @@ class CDPMsgIPGateway(CDPMsgGeneric):
                    IPField("defaultgw", "192.168.0.1")]
 
 
+class CDPIPPrefix(Packet):
+    fields_desc = [
+        IPField("prefix", "192.168.0.1"),
+        ByteField("plen", 24),
+    ]
+
+    def guess_payload_class(self, p):
+        return conf.padding_layer
+
+
 class CDPMsgIPPrefix(CDPMsgGeneric):
     name = "IP Prefix"
     type = 0x0007
     fields_desc = [XShortEnumField("type", 0x0007, _cdp_tlv_types),
                    ShortField("len", 9),
-                   IPField("prefix", "192.168.0.1"),
-                   ByteField("plen", 24)]
+                   PacketListField("prefixes", [], CDPIPPrefix,
+                                   length_from=lambda p: p.len - 4)]
 
 
 class CDPMsgProtoHello(CDPMsgGeneric):