vxlan_gpe_encap: fix packet len error

Change-Id: I294be184764b45777d6e5e44f5d742b2c8732de4
Signed-off-by: Zhiyong Yang <zhiyong.yang@intel.com>
diff --git a/src/vnet/vxlan-gpe/encap.c b/src/vnet/vxlan-gpe/encap.c
index c97972b..e62a84e 100644
--- a/src/vnet/vxlan-gpe/encap.c
+++ b/src/vnet/vxlan-gpe/encap.c
@@ -242,7 +242,7 @@
 	  pkts_encapsulated += 2;
 
 	  len0 = vlib_buffer_length_in_chain (vm, b0);
-	  len1 = vlib_buffer_length_in_chain (vm, b0);
+	  len1 = vlib_buffer_length_in_chain (vm, b1);
 	  stats_n_packets += 2;
 	  stats_n_bytes += len0 + len1;