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

test/patches/scapy-2.4/cdp.patch

@@ -12,7 +12,7 @@ index c8b7f106..7b1ff64d 100644
                      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 @@ index c8b7f106..7b1ff64d 100644
 +                    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: