Currently, if `-asmap` is specified without a filename, bitcoind tries to load
`ip_asn.map` data file.
This change now requires `-asmap=ip_asn.map` or another filename to be
specified explicitly.
The change is intended to make behavior of the option explicit avoid confusion
reported https://github.com/bitcoin/bitcoin/issues/33386 where documentation
specifies a default file which is not actually loaded by default. It was
originally implemented in
https://github.com/bitcoin/bitcoin/pull/33631#issuecomment-3410302383 and
various alternatives are discussed there.
Co-authored-by: Fabian Jahr <fjahr@protonmail.com>
