MINOR: mux-h1: add counters instance to h1c

Add pointer to counters as a member for h1c structure. This pointer is
initialized on h1_init function. This is useful to quickly access and
manipulate the counters inside every h1 functions.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index f875b96..37ee1f1 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -108,6 +108,7 @@
 
 	struct h1s *h1s;                 /* H1 stream descriptor */
 	struct task *task;               /* timeout management task */
+	struct h1_counters *px_counters; /* h1 counters attached to proxy */
 	int idle_exp;                    /* idle expiration date (http-keep-alive or http-request timeout) */
 	int timeout;                     /* client/server timeout duration */
 	int shut_timeout;                /* client-fin/server-fin timeout duration */
@@ -850,11 +851,17 @@
 		h1c->shut_timeout = h1c->timeout = proxy->timeout.server;
 		if (tick_isset(proxy->timeout.serverfin))
 			h1c->shut_timeout = proxy->timeout.serverfin;
+
+		h1c->px_counters = EXTRA_COUNTERS_GET(proxy->extra_counters_be,
+		                                      &h1_stats_module);
 	} else {
 		h1c->shut_timeout = h1c->timeout = proxy->timeout.client;
 		if (tick_isset(proxy->timeout.clientfin))
 			h1c->shut_timeout = proxy->timeout.clientfin;
 
+		h1c->px_counters = EXTRA_COUNTERS_GET(proxy->extra_counters_fe,
+		                                      &h1_stats_module);
+
 		LIST_APPEND(&mux_stopping_data[tid].list,
 		            &h1c->conn->stopping_list);
 	}