goptlib should enforce the `TOR_PT_SERVER_BINDADDR` restriction.
Followup from #21136 (closed).
TOR_PT_SERVER_BINDADDR by spec is limited to one address+port per transport. goptlib should enforce this, and raise an
ENV-ERROR if anyone tries to specify more than one.
I could add code in obfs4proxy to check for this, but it's a spec restriction, so goptlib doing the enforcement seems more appropriate.