MINOR: h1: Change the union h1_sl to use indirect strings to store infos

Instead of using offsets relating to the parsed buffer to store start line
infos, we now use indirect strings. So now, these infos remain valid only if the
origin buffer remains untouched. But it's not a real problem because this union
is used during the parsing and never stored to a later use.
diff --git a/include/types/h1.h b/include/types/h1.h
index c6645fa..af5c896 100644
--- a/include/types/h1.h
+++ b/include/types/h1.h
@@ -23,6 +23,7 @@
 #define _TYPES_H1_H
 
 #include <common/http.h>
+#include <common/ist.h>
 
 /* Legacy version of the HTTP/1 message state, used by the channels, should
  * ultimately be removed.
@@ -177,15 +178,15 @@
 /* basic H1 start line, describes either the request and the response */
 union h1_sl {                          /* useful start line pointers, relative to ->sol */
 	struct {
-		int m, m_l;            /* METHOD, length */
-		int u, u_l;            /* URI, length */
-		int v, v_l;            /* VERSION, length */
+		struct ist m;          /* METHOD */
+		struct ist u;          /* URI */
+		struct ist v;          /* VERSION */
 		enum http_meth_t meth; /* method */
 	} rq;                          /* request line : field, length */
 	struct {
-		int v, v_l;            /* VERSION, length */
-		int c, c_l;            /* CODE, length */
-		int r, r_l;            /* REASON, length */
+		struct ist v;          /* VERSION */
+		struct ist c;          /* CODE */
+		struct ist r;          /* REASON */
 		uint16_t status;       /* status code */
 	} st;                          /* status line : field, length */
 };