lotus-gateway: Fix Filecoin.EthCall

[coderabbitai]

Problem

The Filecoin.EthCall RPC method is broken when accessed through lotus-gateway.

Task

Investigate and fix the Filecoin.EthCall method to work correctly with lotus-gateway.

Context

• Parent issue: lotus-gateway: Fix broken RPC methods #6575
• Identified in: test: add lotus-gateway parity test #6570
• Requested by: @hanabi1224 at test: add lotus-gateway parity test #6570 (comment)
• Filter list: scripts/tests/api_compare/filter-list-gateway