ext4: Use high 16 bits of the block group descriptor's free counts fields

Rename the lower bits with suffix _lo and add helper
to access the values. Also rename bg_itable_unused_hi
to bg_pad as in e2fsprogs.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bcd5ffa..56142ac 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4014,7 +4014,7 @@
 			num = EXT4_INODES_PER_GROUP(sb);
 			if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
 				       EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
-				num -= le16_to_cpu(gdp->bg_itable_unused);
+				num -= ext4_itable_unused_count(sb, gdp);
 			table += num / inodes_per_block;
 			if (end > table)
 				end = table;