Remove SO_REUSEPORT from the RTR socket bind

Remove SO_REUSEPORT from the RTR socket bind

This option is causing portability issues, and I can't figure out why it
was introduced. None of the Github issues mention it, and
6401a4739ac512985158e63499e037dc2f2078db says

> Use SO_REUSEPORT at sockopts so that the RTR port can be reused

But reused when? For what purpose?

I think this might be an allusion to
ac56d70c954caf49382f5f28ff4a017e859e2e0a:

> SO_REUSEADDR sockopt allows to reuse server address and port at once
> when the service has been stoped (or killed).

But that doesn't need SO_REUSEPORT for anything.