cdp: re-enable skipped tests for python3

CDP uses the running sytems host name, which
caused different failures on different systems.
The root cause was an python3 specific error in
checksum calculation.

Type: fix
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: I205436682d46e7e8cbb8c057c03a76dbbcab4d72
diff --git a/src/plugins/cdp/test/test_cdp.py b/src/plugins/cdp/test/test_cdp.py
index c0e5287..27f35c2 100644
--- a/src/plugins/cdp/test/test_cdp.py
+++ b/src/plugins/cdp/test/test_cdp.py
@@ -98,13 +98,9 @@
         self.assert_equal(system[:length], self.device_id[:length],
                           "CDP received invalid device id")
 
-    @unittest.skipIf(sys.version_info[0] > 2,
-                     "not supported in python3/scapy")
     def test_cdp_underflow_tlv(self):
         self.send_bad_packet(3, ".")
 
-    @unittest.skipIf(sys.version_info[0] > 2,
-                     "not supported in python3/scapy")
     def test_cdp_overflow_tlv(self):
         self.send_bad_packet(8, ".")
 
diff --git a/test/patches/scapy-2.4/cdp.patch b/test/patches/scapy-2.4/cdp.patch
index 3248915..de16f5d 100644
--- a/test/patches/scapy-2.4/cdp.patch
+++ b/test/patches/scapy-2.4/cdp.patch
@@ -12,7 +12,7 @@
                      StrLenField("val", "", length_from=lambda x:x.len - 4) ]
  
  
-@@ -178,7 +179,8 @@ class CDPMsgAddr(CDPMsgGeneric):
+@@ -178,5 +179,6 @@ class CDPMsgAddr(CDPMsgGeneric):
  class CDPMsgPortID(CDPMsgGeneric):
      name = "Port ID"
      fields_desc = [ XShortEnumField("type", 0x0003, _cdp_tlv_types),
@@ -20,5 +20,12 @@
 +                    FieldLenField("len", None, "iface", "!H",
 +                                  adjust=lambda pkt, x: x + 4),
                      StrLenField("iface", "Port 1", length_from=lambda x:x.len - 4) ]
- 
- 
+@@ -319,7 +319,7 @@ class _CDPChecksum:
+         This padding is only used for checksum computation.  The original
+         packet should not be altered."""
+         if len(pkt) % 2:
+-            last_chr = pkt[-1]
++            last_chr = pkt[len(pkt)-1:]
+             if last_chr <= b'\x80':
+                 return pkt[:-1] + b'\x00' + last_chr
+             else: