resize2fs: use EXT2_FLAG_64BITS

resize2fs: use EXT2_FLAG_64BITS

By passing EXT2_FLAG_64BITS to ext2fs_open2() we can avoid some
unnecessary redirection in critical paths. While resize2fs does not
currently otherwise support so big filesystems that this would matter,
passing this flag is entirely harmless and only tells libext2fs that
the caller has been recompiled against current headers.

With this change the CPU time needed to shrink a 100G filesystem drops
by 20%.

Signed-off-by: Sami Liedes <sami.liedes@iki.fi>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>