ext4: store maxbytes for bitmapped files and return EFBIG as appropriate

Calculate & store the max offset for bitmapped files, and
catch too-large seeks, truncates, and writes in ext4, shortening
or rejecting as appropriate.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>

diff --cc fs/ext4/file.c
Simple merge

diff --cc fs/ext4/inode.c
Simple merge

diff --cc fs/ext4/super.c
Simple merge

diff --cc include/linux/ext4_fs_sb.h
Simple merge