MINOR: muxes: Don't handle proto upgrade for muxes not supporting it

Several muxes (h2, fcgi, quic) don't support the protocol upgrade. For these
muxes, there is no reason to have code to support it. Thus in the destroy
callback, there is now a BUG_ON() and the release function is simplified
because the connection is always owned by the mux..
3 files changed