When we create a directory with enable compression, all file write into
directory will try to compress.But sometimes we may know, new file
cannot meet compression ratio requirements.
We need a nocompress extension to skip those files to avoid unnecessary
compress page test.

After add nocompress_extension, the priority should be:
dir_flag < comp_extention,nocompress_extension < comp_file_flag,
no_comp_file_flag.

Priority in between FS_COMPR_FL, FS_NOCOMP_FS, extensions:
   * compress_extension=so; nocompress_extension=zip; chattr +c dir;
     touch dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so
     and baz.txt should be compresse, bar.zip should be non-compressed.
     chattr +c dir/bar.zip can enable compress on bar.zip.
   * compress_extension=so; nocompress_extension=zip; chattr -c dir;
     touch dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so
     should be compresse, bar.zip and baz.txt should be non-compressed.
     chattr+c dir/bar.zip; chattr+c dir/baz.txt; can enable compress on
     bar.zip and baz.txt.
Signed-off-by: Fengnan Chang <changfengnan@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>