IPIP and IPv6 fragmentation

- Error where ICMPv6 error code doesn't reset VLIB_TX = -1
  Leading to crash for ICMP generated on tunnelled packets
- Missed setting VNET_BUFFER_F_LOCALLY_ORIGINATED, so
  IP in IPv6 packets never got fragmented.
- Add support for fragmentation of buffer chains.
- Remove support for inner fragmentation in frag code itself.

Change-Id: If9a97301b7e35ca97ffa5c0fada2b9e7e7dbfb27
Signed-off-by: Ole Troan <ot@cisco.com>
diff --git a/src/vpp-api/python/vpp_papi/vpp_stats.py b/src/vpp-api/python/vpp_papi/vpp_stats.py
index 456312b..8c1aaf2 100644
--- a/src/vpp-api/python/vpp_papi/vpp_stats.py
+++ b/src/vpp-api/python/vpp_papi/vpp_stats.py
@@ -134,7 +134,8 @@
         for i in range(rv_len):
             n = ffi.string(rv[i].name).decode()
             e = stat_entry_to_python(self.api, rv[i])
-            stats[n] = e
+            if e != None:
+                stats[n] = e
         return stats
 
     def get_counter(self, name):