[Fix] Update `nconns` in proxy

src/rspamd_proxy.c

 		rspamd_mempool_delete(session->pool);
 	}
 
+	session->worker->nconns--;
+
 	g_free(session);
 }
 
 		return;
 	}
 
+	worker->nconns++;
+
 	session = g_malloc0(sizeof(*session));
 	REF_INIT_RETAIN(session, proxy_session_dtor);
 	session->client_sock = nfd;