BUG/MINOR: event_hdl: fix rid storage type

rid is stored as a uint32_t within struct server, but it was stored as
a signed int within the server event data struct.

Switching from signed int to uint32_t in event_hdl_cb_data_server struct
to make sure it won't overflow.

If 129ecf441 ("MINOR: server/event_hdl: add support for SERVER_ADD and SERVER_DEL events")
is being backported, then this commit should be backported with it.
diff --git a/include/haproxy/server-t.h b/include/haproxy/server-t.h
index d3e49d8..e7f7747 100644
--- a/include/haproxy/server-t.h
+++ b/include/haproxy/server-t.h
@@ -430,7 +430,7 @@
 		char name[64];       /* server name/id */
 		char proxy_name[64]; /* id of proxy the server belongs to */
 		int puid;            /* proxy-unique server ID */
-		int rid;             /* server id revision */
+		uint32_t rid;        /* server id revision */
 		unsigned int flags;  /* server flags */
 	} safe;
 	struct {