ipv6: support [ipv6]:port in client proxy
ipv6: support [ipv6]:port in client proxy

https://libwebsockets.org/pipermail/libwebsockets/2019-March/007840.html
sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets