Implement ioprio_get and ioprio_set decoding

* ioprio.c: New file.
* Makefile.am (strace_SOURCES): Add ioprio.c.
* linux/dummy.h (sys_ioprio_get, sys_ioprio_set): Remove.
* linux/syscall.h (sys_ioprio_get, sys_ioprio_set): New prototypes.
4 files changed