Return a proper error when method is not supported
Some performance tweaks

- The node round-robin mode leads to a significant slow-down in my benchmarks
  for both large & slow requests

- With a larger somaxconn and a larger listen wait queue limit the kernel
  ensures low latencies natively and with lower overhead.

- Current benchmark results: 3000 req/s for a blob containing 'hello world',
  4GBit for a 3mb blob. Both with latencies < 100ms at the 95th percentile.