credit_only credits forwarding (#6509)

* credit_only_credits_forwarding

* whack transfer_now()

* fixup

* bench should retry the airdrop TX

* fixup

* try to make bench-exchange a bit more robust, informative

core/src/packet.rs

@@ -602,7 +602,7 @@ mod tests {
     fn test_to_packets() {
         let keypair = Keypair::new();
         let hash = Hash::new(&[1; 32]);
-        let tx = system_transaction::transfer_now(&keypair, &keypair.pubkey(), 1, hash);
+        let tx = system_transaction::transfer(&keypair, &keypair.pubkey(), 1, hash);
         let rv = to_packets(&vec![tx.clone(); 1]);
         assert_eq!(rv.len(), 1);
         assert_eq!(rv[0].packets.len(), 1);