ip: reassembly fix sanity checks

use correct value for sanity checks

Type: fix

Change-Id: If33db5ce3e4a26f7876c2a67832ca2947563e211
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/src/vnet/ip/reass/ip6_full_reass.c b/src/vnet/ip/reass/ip6_full_reass.c
index 4e9079d..7f56d2c 100644
--- a/src/vnet/ip/reass/ip6_full_reass.c
+++ b/src/vnet/ip/reass/ip6_full_reass.c
@@ -1092,6 +1092,9 @@
 	      next0 = IP6_FULL_REASSEMBLY_NEXT_INPUT;
 	      goto skip_reass;
 	    }
+	  vnet_buffer (b0)->ip.reass.ip6_frag_hdr_offset =
+	    (u8 *) frag_hdr - (u8 *) ip0;
+
 	  if (0 == ip6_frag_hdr_offset (frag_hdr))
 	    {
 	      // first fragment - verify upper-layer is present
@@ -1110,9 +1113,6 @@
 	      next0 = IP6_FULL_REASSEMBLY_NEXT_ICMP_ERROR;
 	      goto skip_reass;
 	    }
-	  vnet_buffer (b0)->ip.reass.ip6_frag_hdr_offset =
-	    (u8 *) frag_hdr - (u8 *) ip0;
-
 	  ip6_full_reass_kv_t kv;
 	  u8 do_handoff = 0;