ext2: avoid rec_len overflow with 64KB block size

With 64KB blocksize, a directory entry can have size 64KB which does not
fit into 16 bits we have for entry length.  So we store 0xffff instead and
convert the value when read from / written to disk.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>