The `Broadcast`/`ResendWalletTransactions` interface is strange:

- it's the node saying to the wallet "Try to submit your unconfirmed transactions to the mempool again"
- it's called in one place by the node, in `SendMessages()` here: https://github.com/bitcoin/bitcoin/blob/c033c4b5cef89a654e4d9d5c5f9bd823871b068b/src/net_processing.cpp#L3515. `SendMessages()` is called on the message handling thread on a loop.
- the actual scheduling of when the wallet sends messages is handled in the `ResendWalletTransactions()` function itself, using the `nNextResend` and `nLastResend` wallet globals (which could as easily be static variables in `ResendWalletTransactions()`).

Therefore the only use of `Broadcast()` is to periodically prod the wallet. The wallet itself decides whether it's time to resend transactions. This could be done by scheduling regular calls to `ResendWalletTransactions()`, in the same way that we schedule regular wallet flushes here: https://github.com/bitcoin/bitcoin/blob/c033c4b5cef89a654e4d9d5c5f9bd823871b068b/src/wallet/init.cpp#L215.

A couple of minor implementation details:

- the call to `Broadcast()` in `SendMessages()` is protected by an if statement `if (!fReindex && !fImporting && !IsInitialBlockDownload()) {`. Those tests could be moved into `ResendWalletTransactions()` (through the `Chain` interface).
- The `Broadcast` notification passes in the `nTimeBestReceived` time of the best block. That could be fetched by `ResendWalletTransactions()` through the `Chain` interface.
{
    LOCK(cs_main);
    if (connman == nullptr) return;
    int64_t time_in_seconds = GetTime();
    EvictExtraOutboundPeers(time_in_seconds);
    if (time_in_seconds > m_stale_tip_check_time) {
        
        
        if (!fImporting && !fReindex && connman->GetNetworkActive() && connman->GetUseAddrmanOutgoing() && TipMayBeStale(consensusParams)) {
            LogPrintf("Potential stale tip detected, will try using extra outbound peer (last tip update: %d seconds ago)\n", time_in_seconds - g_last_tip_update);
            connman->SetTryNewOutboundPeer(true);
        } else if (connman->GetTryNewOutboundPeer()) {
            connman->SetTryNewOutboundPeer(false);
        }
        m_stale_tip_check_time = time_in_seconds + STALE_CHECK_INTERVAL;
    }
}
namespace {
class CompareInvMempoolOrder