net/quinn: Configure QUIC roles (server/client)

QUIC is a server-client protocol (similar to TCP). The current implementation considers quinnquicsink as a QUIC client and quinnquicsrc as a QUIC server. I would like to open a discussion on how to make roles configurable in these elements. The following two options came to my mind:

1. Add new properties to quinnquicsink/quinnquicsrc:
   • set role=client to make the element act as a QUIC client, and role=server to act as a QUIC server
2. Add new elements:
   • similar to TCP, introduce new elements like quinnquicclientsink,quinnquicclientsrc, etc.

I am more on the side of option 1) since it requires less element and code duplication. In addition, we have a working in-house implementation. I am also aware that it might make element configuration slightly more complicated due to extra parameters (e.g., client-address will be availabe for client and server too) that might lead to user confusion.

Comments are welcome.