[wallet] Update the rebroadcast frequency to be ~1/day.

Since the mempool unbroadcast mechanism handles the reattempts for initial
broadcast, the wallet rebroadcast attempts can be much less frequent
(previously ~1/30 min)

src/wallet/wallet.cpp

@@ -1978,7 +1978,8 @@ void CWallet::ResendWalletTransactions()
     // that these are our transactions.
     if (GetTime() < nNextResend || !fBroadcastTransactions) return;
     bool fFirst = (nNextResend == 0);
-    nNextResend = GetTime() + GetRand(30 * 60);
+    // resend 12-36 hours from now, ~1 day on average.
+    nNextResend = GetTime() + (12 * 60 * 60) + GetRand(24 * 60 * 60);
     if (fFirst) return;
 
     // Only do it if there's been a new block since last time

test/functional/wallet_resendwallettransactions.py

@@ -69,9 +69,10 @@ class ResendWalletTransactionsTest(BitcoinTestFramework):
         node.p2ps[1].sync_with_ping()
         assert_equal(node.p2ps[1].tx_invs_received[txid], 0)
 
-        self.log.info("Transaction should be rebroadcast after 30 minutes")
-        # Use mocktime and give an extra 5 minutes to be sure.
-        rebroadcast_time = int(time.time()) + 41 * 60
+        self.log.info("Bump time & check that transaction is rebroadcast")
+        # Transaction should be rebroadcast approximately 24 hours in the future,
+        # but can range from 12-36. So bump 36 hours to be sure.
+        rebroadcast_time = int(time.time()) + 36 * 60 * 60
         node.setmocktime(rebroadcast_time)
         wait_until(lambda: node.p2ps[1].tx_invs_received[txid] >= 1, lock=mininode_lock)