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/cfgparse-listen.c b/src/cfgparse-listen.c
index 18e6770..00b925a 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -2914,6 +2914,7 @@
 
 					curproxy->conn_src.opts &= ~CO_SRC_TPROXY_MASK;
 					curproxy->conn_src.opts |= CO_SRC_TPROXY_DYN;
+					free(curproxy->conn_src.bind_hdr_name);
 					curproxy->conn_src.bind_hdr_name = calloc(1, end - name + 1);
 					curproxy->conn_src.bind_hdr_len = end - name;
 					memcpy(curproxy->conn_src.bind_hdr_name, name, end - name);