libwebsockets

ss: server: allow bind to existing vhost

If the larger application is defining vhosts using lejp-conf JSON, it's
often more convenient to describe the vhost for ss server binding to
that.

If the server policy endpoint (usually used to describe the server
interface bind) begins with '!', take the remainder of the endpoint
string as the name of a preexisting vhost to bind ss server to at
creation-time.