txpool: re-relay txs that haven't been relayed and need to be

Fixes the following circumstance:
1. Wallet submits tx to node.
2. Node adds tx to pool and queues for relay.
3. Node shuts off before the relay executes in the strand.
4. Node restarts.
5. Now, the fix ensures the node will re-relay the tx in the
get_relayable_transactions loop.

Also makes sure that stem txs don't have last_relayed_time set
to max, which would prevent them from ever being re-relayed on
a restart as well.

Context: https://github.com/seraphis-migration/monero/issues/365#issuecomment-4811722029
(cherry picked from commit aa13c6340f0d855d42aed1d9a8bebe76245e0e7c)

src/cryptonote_core/tx_pool.cpp

@@ -300,9 +300,10 @@ namespace cryptonote
         {
           using clock = std::chrono::system_clock;
           auto last_relayed_time = std::numeric_limits<decltype(meta.last_relayed_time)>::max();
-          if (tx_relay == relay_method::forward)
+          if (tx_relay == relay_method::forward || tx_relay == relay_method::stem)
           {
-            last_relayed_time = clock::to_time_t(clock::now() + crypto::random_poisson_seconds{forward_delay_average}());
+            const auto delay = tx_relay == relay_method::forward ? forward_delay_average : dandelionpp_embargo_average;
+            last_relayed_time = clock::to_time_t(clock::now() + crypto::random_poisson_seconds{delay}());
             set_if_less(m_next_check, time_t(last_relayed_time));
           }
           // else the `set_relayed` function will adjust the time accordingly later
@@ -815,6 +816,8 @@ namespace cryptonote
           case relay_method::local:
           case relay_method::fluff:
           case relay_method::block:
+            if (!meta.relayed)
+              break; // if it hasn't been relayed yet, relay it
             if (now - meta.last_relayed_time <= get_relay_delay(meta.last_relayed_time, meta.receive_time))
               return true; // continue to next tx
             break;