MINOR: checks: export a few functions that appear often in trace dumps

The check I/O handler, process_chk_conn and server_warmup are often
present in complex backtraces as they're impacted by locking or I/O
issues. Let's export them so that they resolve cleanly.
diff --git a/src/check.c b/src/check.c
index 2c0a0ac..0528372 100644
--- a/src/check.c
+++ b/src/check.c
@@ -820,7 +820,7 @@
 }
 
 /* This function checks if any I/O is wanted, and if so, attempts to do so */
-static struct task *event_srv_chk_io(struct task *t, void *ctx, unsigned short state)
+struct task *event_srv_chk_io(struct task *t, void *ctx, unsigned short state)
 {
 	struct check *check = ctx;
 	struct conn_stream *cs = check->cs;
@@ -835,7 +835,7 @@
  * Please do NOT place any return statement in this function and only leave
  * via the out_unlock label.
  */
-static struct task *process_chk_conn(struct task *t, void *context, unsigned short state)
+struct task *process_chk_conn(struct task *t, void *context, unsigned short state)
 {
 	struct check *check = context;
 	struct proxy *proxy = check->proxy;
@@ -1107,7 +1107,7 @@
  * reached, the task automatically stops. Note that any server status change
  * must have updated s->last_change accordingly.
  */
-static struct task *server_warmup(struct task *t, void *context, unsigned short state)
+struct task *server_warmup(struct task *t, void *context, unsigned short state)
 {
 	struct server *s = context;