file-posix: x-check-cache-dropped should default to false on reopen

The default value of x-check-cache-dropped is false. There's no reason
to use the previous value as a default in raw_reopen_prepare() because
bdrv_reopen_queue_child() already takes care of putting the old
options in the BDRVReopenState.options QDict.

If x-check-cache-dropped was previously set but is now missing from
the reopen QDict then it should be reset to false.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/file-posix.c

@@ -850,7 +850,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
     }
 
     rs->check_cache_dropped = qemu_opt_get_bool(opts, "x-check-cache-dropped",
-                                                s->check_cache_dropped);
+                                                false);
 
     if (s->type == FTYPE_CD) {
         rs->open_flags |= O_NONBLOCK;