BUILD: xprt: use an initcall to register the transport layers

Transport layers (raw_sock, ssl_sock, xprt_handshake and xprt_quic)
were using 4 constructors and 2 destructors. The 4 constructors were
replaced with INITCALL and the destructors with REGISTER_POST_DEINIT()
so that we do not depend on this anymore.
4 files changed