ip ipsec: Remove IPSec SPI-0 punt reason

Type: fix

There's no call for an SPI-0 punt reason with UDP encap, since
it's only with UDP encap that the ambiguity between IKE or IPSEC
occurs (and SPI=0 determines IKE).

Enhance the punt API to dum ponly the reason requested, so a client
can use this as a get-ID API

Change-Id: I5c6d72b03885e88c489117677e72f1ef5da90dfc
Signed-off-by: Neale Ranns <nranns@cisco.com>
diff --git a/src/vnet/ipsec/ipsec_if_in.c b/src/vnet/ipsec/ipsec_if_in.c
index d1f9d5c..4e93725 100644
--- a/src/vnet/ipsec/ipsec_if_in.c
+++ b/src/vnet/ipsec/ipsec_if_in.c
@@ -74,7 +74,8 @@
       b->error = node->errors[IPSEC_IF_INPUT_ERROR_SPI_0];
       b->punt_reason =
 	ipsec_punt_reason[(ip4->protocol == IP_PROTOCOL_UDP ?
-			   IPSEC_PUNT_IP4_SPI_UDP_0 : IPSEC_PUNT_IP4_SPI_0)];
+			   IPSEC_PUNT_IP4_SPI_UDP_0 :
+			   IPSEC_PUNT_IP4_NO_SUCH_TUNNEL)];
     }
   else
     {
@@ -90,16 +91,9 @@
 			vlib_buffer_t * b,
 			const esp_header_t * esp, u16 offset)
 {
-  if (PREDICT_FALSE (0 == esp->spi))
-    {
-      b->error = node->errors[IPSEC_IF_INPUT_ERROR_NO_TUNNEL];
-      b->punt_reason = ipsec_punt_reason[IPSEC_PUNT_IP6_SPI_0];
-    }
-  else
-    {
-      b->error = node->errors[IPSEC_IF_INPUT_ERROR_NO_TUNNEL];
-      b->punt_reason = ipsec_punt_reason[IPSEC_PUNT_IP6_NO_SUCH_TUNNEL];
-    }
+  b->error = node->errors[IPSEC_IF_INPUT_ERROR_NO_TUNNEL];
+  b->punt_reason = ipsec_punt_reason[IPSEC_PUNT_IP6_NO_SUCH_TUNNEL];
+
   vlib_buffer_advance (b, -offset);
   return (IPSEC_INPUT_NEXT_PUNT);
 }