libext2fs: provide functions to safely access name_len and file_type

libext2fs: provide functions to safely access name_len and file_type

Accessing name_len (and file_type) in ext4_dir_entry structure is
somewhat problematic because on big endian architecture we need to now
whether we are really dealing with ext4_dir_entry (which has u16
name_len which needs byte swapping) or ext4_dir_entry_2 (which has u8
name_len which must not be byte swapped).

Currently the code is somewhat surprising and name_len is always
treated as u16 and byte swapped (flag EXT2_DIRBLOCK_V2_STRUCT isn't
ever used) and then masking of name_len is used to access real
name_len or file_type. Doing things this way in applications using
libext2fs is unexpected to say the least (more natural is to type
struct ext4_dir_entry * to struct ext4_dir_entry_2 * but that gives
wrong results on big endian architectures. So provide helper functions
that give endian-safe access to these fields. Also convert users in
e2fsprogs to use these functions.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>