Limit conn: fixed counter leak on memory allocation errors.

Limit conn: fixed counter leak on memory allocation errors.

Previously, if ngx_pool_cleanup_add() failed, already incremented
connection counter was left as is, eventually resulting in unexpected
connection limiting or shared memory exhaustion.  Fix is to decrement
the counter by calling the cleanup handler with data on stack.

Signed-off-by: Elijah Zupancic <e.zupancic@f5.com>
Origin: <https://freenginx.org/hg/nginx/rev/722e252fcabe6413eb63555890273d7b0e7fc132>