The block height validation is gated by the startup option
`con_blockheightinheader`, accesible in custom chains only
using option `chain=<name>`. Only if set to true will this
field be (de)serialized and evaluated in consensus logic.
Otherwise the field is simply ignored, other than being
stored in memory as the default value 0.
fa6ab8ada1 rpc: Return more specific reject reason for submitblock (MarcoFalke)
Pull request description:
The second commit in #13439 made the `TODO` in the first commit impossible to solve.
The meaning of `fNewBlock` changed from "This is the first time we process this block" to "We are about to write the new *valid* block".
So whenever `fNewBlock` is true, the block was valid. And whenever the `fNewBlock` is false, the block is either valid or invalid. If it was valid and not new, we know it is a `"duplicate"`. In all other cases, the `BIP22ValidationResult()` will return the reason why it is invalid.
Tree-SHA512: 4b6edf7a912339c3acb0fccfabbdd6d812a0321fb1639c244c2714e58dc119aa2b8c6bf8f7d61ea609a1b861bbc23f920370fcf989c48452721e259a8ce93d24
