[BUG]
Currently btrfs can create subvolume with an invalid qgroup inherit
without triggering any error:

  # mkfs.btrfs -O quota -f $dev
  # mount $dev $mnt
  # btrfs subvolume create -i 2/0 $mnt/subv1
  # btrfs qgroup show -prce --sync $mnt
  Qgroupid    Referenced    Exclusive   Path
  --------    ----------    ---------   ----
  0/5           16.00KiB     16.00KiB   <toplevel>
  0/256         16.00KiB     16.00KiB   subv1

[CAUSE]
We only do a very basic size check for btrfs_qgroup_inherit structure,
but never really verify if the values are correct.

Thus in btrfs_qgroup_inherit() function, we have to skip non-existing
qgroups, and never return any error.

[FIX]
Fix the behavior and introduce extra checks:

- Introduce early check for btrfs_qgroup_inherit structure
  Not only the size, but also all the qgroup ids would be verified.

  And the timing is very early, so we can return error early.
  This early check is very important for snapshot creation, as snapshot
  is delayed to transaction commit.

- Drop support for btrfs_qgroup_inherit::num_ref_copies and
  num_excl_copies
  Those two members are used to specify to copy refr/excl numbers from
  other qgroups.
  This would definitely mark qgroup inconsistent, and btrfs-progs has
  dropped the support for them for a long time.
  It's time to drop the support for kernel.

- Verify the supported btrfs_qgroup_inherit::flags
  Just in case we want to add extra flags for btrfs_qgroup_inherit.

Now above subvolume creation would fail with -ENOENT other than silently
ignore the non-existing qgroup.

CC: stable@vger.kernel.org # 6.7+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>