bugfix: respect max retry after using balancer pool

[tzssangglass]

In the balancer phase, when obtaining a connection from the upstream connection pool, the cached attribute of the peer connection is set to 1(pc->cached = 1;), indicating that the connection is obtained from the cache.

If an error occurs during the use of this connection, such as "upstream prematurely closed connection" the system will increase the tries attribute of the peer connection by executing u->peer.tries++.

This PR restores tries by callbacks to the balancer when u->peer.tries++ is unexpectedly set.

I hereby granted the copyright of the changes in this pull request
to the authors of this lua-nginx-module project.

[tzssangglass]

sister PR:

• ngx-build: add balancer_pool_max_retry.patch openresty-devel-utils#54
• bugfix: respect max retry after using balancer pool openresty#986

[zhuizhuhaomeng]

/home/travis/build/openresty/lua-nginx-module/src/ngx_http_lua_balancer.c: In function ‘ngx_http_lua_balancer_notify_peer’:
/home/travis/build/openresty/lua-nginx-module/src/ngx_http_lua_balancer.c:747:17: error: ‘NGX_HTTP_UPSTREAM_NOTIFY_CACHED_CONNECTION_ERROR’ undeclared (first use in this function); did you mean ‘NGX_HTTP_UPSTREAM_IGN_CACHE_CONTROL’?
  747 |     if (type == NGX_HTTP_UPSTREAM_NOTIFY_CACHED_CONNECTION_ERROR) {
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                 NGX_HTTP_UPSTREAM_IGN_CACHE_CONTROL
/home/travis/build/openresty/lua-nginx-module/src/ngx_http_lua_balancer.c:747:17: note: each undeclared identifier is reported only once for each function it appears in

[tzssangglass]

/home/travis/build/openresty/lua-nginx-module/src/ngx_http_lua_balancer.c: In function ‘ngx_http_lua_balancer_notify_peer’:
/home/travis/build/openresty/lua-nginx-module/src/ngx_http_lua_balancer.c:747:17: error: ‘NGX_HTTP_UPSTREAM_NOTIFY_CACHED_CONNECTION_ERROR’ undeclared (first use in this function); did you mean ‘NGX_HTTP_UPSTREAM_IGN_CACHE_CONTROL’?
747 | if (type == NGX_HTTP_UPSTREAM_NOTIFY_CACHED_CONNECTION_ERROR) {
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| NGX_HTTP_UPSTREAM_IGN_CACHE_CONTROL
/home/travis/build/openresty/lua-nginx-module/src/ngx_http_lua_balancer.c:747:17: note: each undeclared identifier is reported only once for each function it appears in

https://github.com/openresty/openresty/pull/986/files