[infiniband] Allow SRP reconnection attempts even after reporting failures

With iSCSI, connection attempts are expensive; it may take many
seconds to determine that a connection will fail.  SRP connection
attempts are much less expensive, so we may as well avoid the
"optimisation" of declaring a state of permanent failure after a
certain number of attempts.  This allows a gPXE SRP initiator to
resume operations after an arbitrary amount of SRP target downtime.

src/drivers/block/srp.c

 	/* Clear session state */
 	srp->state = 0;
 
-	/* Increment retry count */
-	srp->retry_count++;
-
-	/* If we have reached the retry limit, permanently abort the
-	 * session.
-	 */
+	/* If we have reached the retry limit, report the failure */
 	if ( srp->retry_count >= SRP_MAX_RETRIES ) {
-		srp->instant_rc = rc;
 		srp_scsi_done ( srp, rc );
 		return;
 	}
 
-	/* Otherwise, try to reopen the connection */
+	/* Otherwise, increment the retry count and try to reopen the
+	 * connection
+	 */
+	srp->retry_count++;
 	srp_login ( srp );
 }
 
 	struct srp_device *srp =
 		container_of ( scsi->backend, struct srp_device, refcnt );
 
-	/* Return instant failure, if we have already aborted the session */
-	if ( srp->instant_rc )
-		return srp->instant_rc;
-
 	/* Store SCSI command */
 	if ( srp->command ) {
 		DBGC ( srp, "SRP %p cannot handle concurrent SCSI commands\n",

src/include/gpxe/srp.h

 	unsigned int state;
 	/** Retry counter */
 	unsigned int retry_count;
-	/** Instant return status code
-	 *
-	 * Used to avoid retrying the connection on every new SCSI
-	 * command after the retry count has been exceeded.
-	 */
-	int instant_rc;
 	/** Current SCSI command */
 	struct scsi_command *command;