Add notification at request completion

Another functionality that was missing from the original implementation was the generation of a notification upon request completion. Each aiocbp has the field aio_sigevent that specifies the type of notification that should occur when a request is completed. The implementation ignored this field and did not deliver any notification of completion.

To add support for this feature, I created two new functions:

• rtems_aio_check_sigevent(). This function is used to validate the content af a sigevent struct. The function is used inside the methods that enqueue requests, namely aio_read(), aio_write() and aio_fsync() to verify the correctness of the passed data. The function takes as pointer to a sigevent struct and then returns an integer. The value returned is 1 if the sigevent struct is valid, 0 otherwise.

• rtems_aio_notify(). This is the function that generated the notification. This function is called after each request has been processed, in the future i belive this function will also be used to generate a notification when a list of requests, enqueued with lio_listio(), is completed. This function takes as input pointer to a sigevent struct ( assumed to be not NULL ) and generates the notification. The notification is generated as specified by the POSIX Specifications.

To verify that the code was working i added a new test, psxaio04. ` To get feedback on the code and then merge the changes, I opened MR118. From the review process did not emerge major issues with my work, but my mentors ponted oput some aspecs taht could be improved. After fixing those issues and correcting every foratting error the code got merged.