api: Increase the maximum object size limit from 5GiB to 16GiB. (#3834)

The globalMaxObjectSize limit is instilled in S3 spec perhaps
due to certain limitations on S3 infrastructure. For minio we
don't have such limitations and we can stream a larger file
instead.

So we are going to bump this limit to 16GiB.

Fixes #3825

cmd/admin-handlers_test.go

@@ -1239,16 +1239,16 @@ func TestWriteSetConfigResponse(t *testing.T) {
 	}
 
 	testPeers := []adminPeer{
-		adminPeer{
+		{
 			addr: "localhost:9001",
 		},
-		adminPeer{
+		{
 			addr: "localhost:9002",
 		},
-		adminPeer{
+		{
 			addr: "localhost:9003",
 		},
-		adminPeer{
+		{
 			addr: "localhost:9004",
 		},
 	}