e2fsck: fix indexed dir rehash failure with metadata_csum enabled

e2fsck: fix indexed dir rehash failure with metadata_csum enabled

E2fsck directory rehashing code can fail with ENOSPC due to a bug in
ext2fs_htree_intnode_maxrecs() which fails to take metadata checksum
into account and thus e.g. e2fsck can decide to create 1 indirect level
of index tree when two are actually needed. Fix the logic to account for
metadata checksum.

Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>