ext4: make block group checksums use metadata_csum algorithm

metadata_csum supersedes uninit_bg.  Convert the ROCOMPAT uninit_bg
flag check to a helper function that covers both, and make the
checksum calculation algorithm use either crc16 or the metadata_csum
chosen algorithm depending on which flag is set.  Print a warning if
we try to mount a filesystem with both feature flags set.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 16a6735..7bccdf3 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3584,8 +3584,7 @@
 				b = table;
 			end = b + EXT4_SB(sb)->s_inode_readahead_blks;
 			num = EXT4_INODES_PER_GROUP(sb);
-			if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
-				       EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
+			if (ext4_has_group_desc_csum(sb))
 				num -= ext4_itable_unused_count(sb, gdp);
 			table += num / inodes_per_block;
 			if (end > table)