Check for transaction forwarding delay to detect an expired transaction before forwarding it (#4249)

Also refactored code for forwarding packets, and added test for it

sdk/src/timing.rs

@@ -24,6 +24,10 @@ pub const MAX_HASH_AGE_IN_SECONDS: usize = 120;
 // This must be <= MAX_HASH_AGE_IN_SECONDS, otherwise there's risk for DuplicateSignature errors
 pub const MAX_RECENT_BLOCKHASHES: usize = MAX_HASH_AGE_IN_SECONDS;
 
+/// This is maximum time consumed in forwarding a transaction from one node to next, before
+/// it can be processed in the target node
+pub const MAX_TRANSACTION_FORWARDING_DELAY: usize = 3;
+
 pub fn duration_as_ns(d: &Duration) -> u64 {
     d.as_secs() * 1_000_000_000 + u64::from(d.subsec_nanos())
 }