[infiniband] Disambiguate CM connection rejection reasons

There is diagnostic value in being able to disambiguate between the
various reasons why an IB CM has rejected a connection attempt.  In
particular, reason 8 "invalid service ID" can be used to identify an
incorrect SRP service_id root-path component, and reason 28 "consumer
reject" corresponds to a genuine SRP login rejection IU, which can be
passed up to the SRP layer.

For rejection reasons other than "consumer reject", we should not pass
through the private data, since it is most likely generated by the CM
without any protocol-specific knowledge.

src/include/gpxe/ib_mad.h

@@ -402,6 +402,11 @@ struct ib_cm_connect_reject {
 	uint8_t private_data[148];
 } __attribute__ (( packed ));
 
+/** CM rejection reasons */
+#define IB_CM_REJECT_BAD_SERVICE_ID	8
+#define IB_CM_REJECT_STALE_CONN		10
+#define IB_CM_REJECT_CONSUMER		28
+
 /** A communication management connection reply
  *
  * Defined in section 12.6.8 of the IBA.