REORG: stats: export some functions

Un-mark stats_dump_one_line and stats_putchk as static and export them
in the header file. These functions will be reusable by other components to
print their statistics.

This patch is needed to extend stat support to components other than
proxies objects.
diff --git a/src/stats.c b/src/stats.c
index c306bfc..9b2e911 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -259,7 +259,7 @@
 
 static void stats_dump_json_schema(struct buffer *out);
 
-static int stats_putchk(struct channel *chn, struct htx *htx, struct buffer *chk)
+int stats_putchk(struct channel *chn, struct htx *htx, struct buffer *chk)
 {
 	if (htx) {
 		if (chk->data >= channel_htx_recv_max(chn, htx))
@@ -1381,7 +1381,7 @@
 	return 1;
 }
 
-static int stats_dump_one_line(const struct field *stats, struct proxy *px, struct appctx *appctx)
+int stats_dump_one_line(const struct field *stats, struct proxy *px, struct appctx *appctx)
 {
 	int ret;