Dont let user set as FR special ethereum address

[Marketen]

We let user add as default FR 0x1000000000000000000000000000000000000000, but it is in fact another burn address, just like 0x0000...0000. We should not let user use this FR.

Consensus client lighthouse defaults to burn address when FR 0x1000...0000 is set and prints a warning. This could cause trouble like crashes in the future, if consensus clients are more strict about this:

[WARN - entrypoint] Fee recipient address is invalid. It should be an Ethereum address
[WARN - entrypoint] Setting the fee recipient address to the burn address