wallet, mempool: propagete checkChainLimits error message to wallet

Update CheckPackageLimits to use util::Result to pass the error message
instead of out parameter.

Also update test to reflect the error message from `CTxMempool`
`CheckPackageLimits` output.

test/functional/wallet_basic.py

@@ -639,7 +639,7 @@ class WalletTest(BitcoinTestFramework):
 
         node0_balance = self.nodes[0].getbalance()
         # With walletrejectlongchains we will not create the tx and store it in our wallet.
-        assert_raises_rpc_error(-6, "Transaction has too long of a mempool chain", self.nodes[0].sendtoaddress, sending_addr, node0_balance - Decimal('0.01'))
+        assert_raises_rpc_error(-6, f"too many unconfirmed ancestors [limit: {chainlimit * 2}]", self.nodes[0].sendtoaddress, sending_addr, node0_balance - Decimal('0.01'))
 
         # Verify nothing new in wallet
         assert_equal(total_txs, len(self.nodes[0].listtransactions("*", 99999)))