Disable wallet fallbackfee by default on mainnet

src/wallet/test/wallet_test_fixture.cpp

@@ -11,6 +11,7 @@ WalletTestingSetup::WalletTestingSetup(const std::string& chainName):
     TestingSetup(chainName)
 {
     bitdb.MakeMock();
+    g_wallet_allow_fallback_fee = true;
 
     bool fFirstRun;
     g_address_type = OUTPUT_TYPE_DEFAULT;