BUG/MINOR: config: fix leak on proxy.conn_src.bind_hdr_name

Leak for parsing of option usesrc of the source keyword.

This can be backported to 1.8.

(cherry picked from commit 69c5c3ab330584f9c53e2cf7c86af371a84f104d)
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/src/haproxy.c b/src/haproxy.c
index 6435fbe..72671ab 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -2504,6 +2504,9 @@
 		free(p->rdp_cookie_name);
 		free(p->invalid_rep);
 		free(p->invalid_req);
+#if defined(CONFIG_HAP_TRANSPARENT)
+		free(p->conn_src.bind_hdr_name);
+#endif
 		if (p->conf.logformat_string != default_http_log_format &&
 		    p->conf.logformat_string != default_tcp_log_format &&
 		    p->conf.logformat_string != clf_http_log_format)