[wallet] Refactor CWalletTx::RelayWalletTransaction()

This refactors the CWalletTx::RelayWalletTransaction() function to be
clearer and adds comments. It also makes two minor behavior
changes:

- no longer assert if fBroadcastTransactions is false. Just return false
from the function.
- no longer print the relay message if p2pEnabled is set to false (since
the transaction is not actually relayed).

src/wallet/wallet.cpp

@@ -1896,20 +1896,25 @@ void CWallet::ReacceptWalletTransactions(interfaces::Chain::Lock& locked_chain)
 
 bool CWalletTx::RelayWalletTransaction(interfaces::Chain::Lock& locked_chain)
 {
-    assert(pwallet->GetBroadcastTransactions());
-    if (!IsCoinBase() && !isAbandoned() && GetDepthInMainChain(locked_chain) == 0)
-    {
-        CValidationState state;
-        /* GetDepthInMainChain already catches known conflicts. */
-        if (InMempool() || AcceptToMemoryPool(locked_chain, state)) {
-            pwallet->WalletLogPrintf("Relaying wtx %s\n", GetHash().ToString());
-            if (pwallet->chain().p2pEnabled()) {
-                pwallet->chain().relayTransaction(GetHash());
-                return true;
-            }
-        }
-    }
-    return false;
+    // Can't relay if wallet is not broadcasting
+    if (!pwallet->GetBroadcastTransactions()) return false;
+    // Don't relay coinbase transactions outside blocks
+    if (IsCoinBase()) return false;
+    // Don't relay abandoned transactions
+    if (isAbandoned()) return false;
+    // Don't relay conflicted or already confirmed transactions
+    if (GetDepthInMainChain(locked_chain) != 0) return false;
+    // Don't relay transactions that aren't accepted to the mempool
+    CValidationState unused_state;
+    if (!InMempool() && !AcceptToMemoryPool(locked_chain, unused_state)) return false;
+    // Don't try to relay if the node is not connected to the p2p network
+    if (!pwallet->chain().p2pEnabled()) return false;
+
+    // Try to relay the transaction
+    pwallet->WalletLogPrintf("Relaying wtx %s\n", GetHash().ToString());
+    pwallet->chain().relayTransaction(GetHash());
+
+    return true;
 }
 
 std::set<uint256> CWalletTx::GetConflicts() const

src/wallet/wallet.h

@@ -535,7 +535,7 @@ public:
 
     int64_t GetTxTime() const;
 
-    // RelayWalletTransaction may only be called if fBroadcastTransactions!
+    // Pass this transaction to the node to relay to its peers
     bool RelayWalletTransaction(interfaces::Chain::Lock& locked_chain);
 
     /** Pass this transaction to the mempool. Fails if absolute fee exceeds absurd fee. */