loop-util: restart loop_configure and reopen FD when O_DIRECT fails

loop-util: restart loop_configure and reopen FD when O_DIRECT fails

On kernel 5.10.178, when a squashfs file is stored on an EXT4 filesystem
backed by a dm-crypt volume, dissecting fails:

$ SYSTEMD_LOG_LEVEL=debug systemd-dissect /var/foo/bar.raw
Opened '/var/foo/bar.raw' in O_RDONLY access mode, with O_DIRECT enabled.
Couldn't find any partition table to derive sector size of.
loop2: Acquired exclusive lock.
Could not enable direct IO mode, proceeding in buffered IO mode.
Successfully acquired /dev/loop2, devno=7:2, nr=2, diskseq=87
Opened /dev/loop2 (fd=3, whole_block_devnum=7:2, diskseq=87).
      Name: bar.raw
      Size: 67.2M
 Sec. Size: 512
     Arch.: n/a

Successfully forked off '(sd-dissect)' as PID 4110.
Mounting /proc/self/fd/3 (squashfs) on /tmp/dissect-Zk3K5F (MS_RDONLY|MS_NODEV "")...
Failed to mount /proc/self/fd/3 (type squashfs) on /tmp/dissect-Zk3K5F (MS_RDONLY|MS_NODEV ""): Input/output error
Failed to mount dissected image: Input/output error
Failed to read /etc/hostname of image: No such file or directory
/etc/machine-id file of image is empty.
Failed to read has-init-system boolean: Input/output error
(sd-dissect) failed with exit status 1.
Failed to acquire image metadata: Input/output error

The kernel shows I/O errors:

kernel: blk_update_request: I/O error, dev loop2, sector 0 op 0x0:(READ) flags 0x800 phys_seg 1 prio class 0
kernel: SQUASHFS error: Failed to read block 0x0: -5
kernel: unable to read squashfs_super_block

This is independent of a particular filesystem and can be reproduced
reliably in my setup, starting from freshly formatted disks.

Instead of continuing when O_DIRECT fails, start over the setup
process without the flag, including opening a new FD, to make the
kernel happy.