317f2cb3f4499afbaa63e3cac80567744f12c95b test: Check RPC settxfee errors (João Barbosa)
48618daf262b84c2e2f7322b5ca14375d7d68b64 Add checks for settxfee reasonableness (Anthony Towns)
Pull request description:
When using the `settxfee` RPC, the value is silently ignored if it is less than either than minrelaytxfee or the wallet's mintxfee. This adds an error response if that's going to happen, but still allows "settxfee 0" to deliberately default to the minimum value.
Backport of Core PR13988
Note: we don't have a wallet_bumpfee.py test, so the second commit (https://github.com/bitcoin/bitcoin/pull/13988/commits/317f2cb3f4499afbaa63e3cac80567744f12c95b) was added to rpc_estimatefee.py because it seemed to be the most closely related test