[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/include/gpxe/srp.h

@@ -828,12 +828,6 @@ struct srp_device {
 	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;