fix for omnipath: changing gaspi_notification_id from unsigned int to byte...

fix for omnipath: changing gaspi_notification_id from unsigned int to byte length, because omnipath writes single bytes at a time, which can result in races because (a) unexpected notification value is read out (b) zero value after reset is filled, bug fix: restrict the notification value to byte length which can not be overwritten: fix has been tested on Omnipath system at kraken.cerfacs.fr