MDEV-15728 main.thread_id_overflow fails in ps-protocol

mark CONNECTION_ID() as returning *unsigned* number

mysql-test/main/func_hybrid_type.result

@@ -3745,11 +3745,11 @@ IF(0,connection_id(),connection_id()) AS c4;
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `c0` int(10) NOT NULL,
-  `c1` int(10) NOT NULL,
-  `c2` int(10) NOT NULL,
-  `c3` int(10) NOT NULL,
-  `c4` int(10) NOT NULL
+  `c0` int(10) unsigned NOT NULL,
+  `c1` int(10) unsigned NOT NULL,
+  `c2` int(10) unsigned NOT NULL,
+  `c3` int(10) unsigned NOT NULL,
+  `c4` int(10) unsigned NOT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1;
 #

sql/item_func.h

@@ -849,7 +849,7 @@ class Item_func_connection_id :public Item_long_func
   longlong value;
 
 public:
-  Item_func_connection_id(THD *thd): Item_long_func(thd) {}
+  Item_func_connection_id(THD *thd): Item_long_func(thd) { unsigned_flag=1; }
   const char *func_name() const { return "connection_id"; }
   void fix_length_and_dec();
   bool fix_fields(THD *thd, Item **ref);