ip: reassembly: drop zero length fragments

Zero length fragments are invalid and should be dropped. This patch adds
that.

Type: improvement
Change-Id: Ic6466c39ca8bf376efe06bb3b7f5d7f1ae812866
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/src/vnet/ip/ip6_error.h b/src/vnet/ip/ip6_error.h
index 8546b4a..6e5df0e 100644
--- a/src/vnet/ip/ip6_error.h
+++ b/src/vnet/ip/ip6_error.h
@@ -89,6 +89,7 @@
   _ (REASS_NO_BUF, "out of buffers (drop)")                             \
   _ (REASS_TIMEOUT, "fragments dropped due to reassembly timeout")      \
   _ (REASS_INTERNAL_ERROR, "drops due to internal reassembly error")    \
+  _ (REASS_INVALID_FRAG_LEN, "invalid fragment length")    \
   _ (REASS_UNSUPP_IP_PROTO, "unsupported ip protocol")
 
 // clang-format on