zram: add size class equals check into recompression

It makes no sense for us to recompress the object if it will be in the
same size class.  We anyway don't get any memory gain.  But, at the same
time, we get a CPU time overhead when inserting this object into zspage
and decompressing it afterwards.

[senozhatsky: rebased and fixed conflicts]
Link: https://lkml.kernel.org/r/20221109115047.2921851-9-senozhatsky@chromium.org


Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>