btrfs: include delalloc related info in dump space info tracepoint

In order to debug delalloc flushing issues I added delalloc_bytes and
ordered_bytes to this tracepoint to see if they were non-zero when we
were going ENOSPC. This was valuable for me and showed me cases where we
weren't waiting on ordered extents properly. In order to add this to the
tracepoint we need to take away the const modifier for fs_info, as
percpu_sum_counter_positive() will change the counter when it adds up
the percpu buckets.  This is needed to make sure we're getting accurate
information at these tracepoints, as the wrong information could send us
down the wrong path when debugging problems.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>