BUG/MINOR: http: Use the global value to limit the number of parsed headers

Instead of using the macro MAX_HTTP_HDR to limit the number of headers parsed
before throwing an error, we now use the custom global variable
global.tune.max_http_hdr.

This patch must be backported to 1.9.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index cbab1c4..2a6e401 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -958,7 +958,7 @@
 				 struct buffer *buf, size_t *ofs, size_t max)
 {
 	struct htx_sl *sl;
-	struct http_hdr hdrs[MAX_HTTP_HDR];
+	struct http_hdr hdrs[global.tune.max_http_hdr];
 	union h1_sl h1sl;
 	unsigned int flags = HTX_SL_F_NONE;
 	size_t used;
@@ -1302,7 +1302,7 @@
 static size_t h1_process_trailers(struct h1s *h1s, struct h1m *h1m, struct htx *htx,
 				  struct buffer *buf, size_t *ofs, size_t max)
 {
-	struct http_hdr hdrs[MAX_HTTP_HDR];
+	struct http_hdr hdrs[global.tune.max_http_hdr];
 	struct h1m tlr_h1m;
 	int ret = 0;