MINOR: backend: make the header hash use arg_opt1 for use_domain_only

This is only a boolean extra arg. Let's map it to arg_opt1 and remove
hh_match_domain from struct proxy.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 448b5a2..1e4115e 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -323,7 +323,6 @@
 	int  uri_len_limit;			/* character limit for uri balancing algorithm */
 	int  uri_dirs_depth1;			/* directories+1 (slashes) limit for uri balancing algorithm */
 	int  uri_whole;				/* if != 0, calculates the hash from the whole uri. Still honors the len_limit and dirs_depth1 */
-	int  hh_match_domain;			/* toggle use of special match function */
 	char *capture_name;			/* beginning of the name of the cookie to capture */
 	int  capture_namelen;			/* length of the cookie name to match */
 	int  capture_len;			/* length of the string to be captured */
diff --git a/src/backend.c b/src/backend.c
index 7a1acec..cc4eb97 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -394,7 +394,8 @@
  * performance by avoiding bounces between servers in contexts where sessions
  * are shared but cookies are not usable. If the parameter is not found, NULL
  * is returned. If any server is found, it will be returned. If no valid server
- * is found, NULL is returned.
+ * is found, NULL is returned. When lbprm.arg_opt1 is set, the hash will only
+ * apply to the middle part of a domain name ("use_domain_only" option).
  */
 static struct server *get_server_hh(struct stream *s, const struct server *avoid)
 {
@@ -429,7 +430,7 @@
 	 */
 	len = ctx.vlen;
 	p = (char *)ctx.line + ctx.val;
-	if (!px->hh_match_domain) {
+	if (!px->lbprm.arg_opt1) {
 		hash = gen_hash(px, p, len);
 	} else {
 		int dohash = 0;
@@ -1802,14 +1803,14 @@
 		free(curproxy->lbprm.arg_str);
 		curproxy->lbprm.arg_len = end - beg;
 		curproxy->lbprm.arg_str = my_strndup(beg, end - beg);
-		curproxy->hh_match_domain = 0;
+		curproxy->lbprm.arg_opt1 = 0;
 
 		if (*args[1]) {
 			if (strcmp(args[1], "use_domain_only")) {
 				memprintf(err, "%s only accepts 'use_domain_only' modifier (got '%s').", args[0], args[1]);
 				return -1;
 			}
-			curproxy->hh_match_domain = 1;
+			curproxy->lbprm.arg_opt1 = 1;
 		}
 	}
 	else if (!strncmp(args[0], "rdp-cookie", 10)) {
diff --git a/src/cfgparse-listen.c b/src/cfgparse-listen.c
index 9774bba..cdeefd0 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -479,8 +479,6 @@
 			curproxy->uri_len_limit   = defproxy.uri_len_limit;
 			curproxy->uri_dirs_depth1 = defproxy.uri_dirs_depth1;
 
-			curproxy->hh_match_domain  = defproxy.hh_match_domain;
-
 			if (defproxy.conn_src.iface_name)
 				curproxy->conn_src.iface_name = strdup(defproxy.conn_src.iface_name);
 			curproxy->conn_src.iface_len = defproxy.conn_src.iface_len;