ext4: disallow modifying DAX inode flag if inline_data has been set

inline_data is mutually exclusive to DAX so enabling both of them triggers
the following issue:
------------------------------------------
# mkfs.ext4 -F -O inline_data /dev/pmem1
...
# mount /dev/pmem1 /mnt
# echo 'test' >/mnt/file
# lsattr -l /mnt/file
/mnt/file                    Inline_Data
# xfs_io -c "chattr +x" /mnt/file
# xfs_io -c "lsattr -v" /mnt/file
[dax] /mnt/file
# umount /mnt
# mount /dev/pmem1 /mnt
# cat /mnt/file
cat: /mnt/file: Numerical result out of range
------------------------------------------

Fixes: b383a73f ("fs/ext4: Introduce DAX inode flag")
Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20200828084330.15776-1-yangx.jy@cn.fujitsu.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -492,7 +492,7 @@ struct flex_groups {
 
 /* Flags which are mutually exclusive to DAX */
 #define EXT4_DAX_MUT_EXCL (EXT4_VERITY_FL | EXT4_ENCRYPT_FL |\
-			   EXT4_JOURNAL_DATA_FL)
+			   EXT4_JOURNAL_DATA_FL | EXT4_INLINE_DATA_FL)
 
 /* Mask out flags that are inappropriate for the given type of inode. */
 static inline __u32 ext4_mask_flags(umode_t mode, __u32 flags)