reassembly: replace asserts with error counters

Change-Id: Iaa39aea990bc04147f6a049215e990a567d30106
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 cc5afb9..6a20de4 100644
--- a/src/vnet/ip/ip6_error.h
+++ b/src/vnet/ip/ip6_error.h
@@ -81,7 +81,8 @@
   _ (REASS_DUPLICATE_FRAGMENT, "duplicate fragments")                   \
   _ (REASS_OVERLAPPING_FRAGMENT, "overlapping fragments")               \
   _ (REASS_LIMIT_REACHED, "drops due to concurrent reassemblies limit") \
-  _ (REASS_TIMEOUT, "fragments dropped due to reassembly timeout")
+  _ (REASS_TIMEOUT, "fragments dropped due to reassembly timeout")      \
+  _ (REASS_INTERNAL_ERROR, "drops due to internal reassembly error")
 
 typedef enum
 {