loop.c: enhance loop ioctl parser

loop.c: enhance loop ioctl parser

Decode as much data on entering syscall as possible.

* loop.c: Include <linux/ioctl.h> instead of <sys/ioctl.h>.
Update for RVAL_DECODED.
(decode_loop_info, decode_loop_info64): New functions.
(loop_ioctl): Use them.  Decode LOOP_SET_STATUS, LOOP_SET_STATUS64,
LOOP_SET_FD, LOOP_CHANGE_FD, LOOP_CTL_ADD and LOOP_CTL_REMOVE on
entering syscall.
Print LOOP_SET_FD and LOOP_CHANGE_FD arguments using printfd.