Improve Stringer interface on acBalancerWrapper to allow human identi…

…fication of which SubConn is used

Signed-off-by: Yolan Romailler <anomalroil@users.noreply.github.com>

balancer_wrapper.go

@@ -261,7 +261,7 @@ func (acbw *acBalancerWrapper) updateState(s connectivity.State, err error) {
 }
 
 func (acbw *acBalancerWrapper) String() string {
-	return fmt.Sprintf("SubConn(id:%d)", acbw.ac.channelz.ID)
+	return fmt.Sprintf("SubConn(id:%d;addr:%s)", acbw.ac.channelz.ID, acbw.ac.curAddr.Addr)
 }
 
 func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {