MEDIUM: ssl_sock: implement ssl_sock_prepare_bind_conf()

Instead of hard-coding all SSL preparation in cfgparse.c, we now register
this new function as the transport layer's prepare_bind_conf() and call it
only when definied. This removes some non-obvious SSL-specific code from
cfgparse.c as well as a #ifdef.
diff --git a/include/proto/ssl_sock.h b/include/proto/ssl_sock.h
index 119368a..eea5344 100644
--- a/include/proto/ssl_sock.h
+++ b/include/proto/ssl_sock.h
@@ -45,6 +45,7 @@
 int ssl_sock_handshake(struct connection *conn, unsigned int flag);
 int ssl_sock_prepare_ctx(struct bind_conf *bind_conf, SSL_CTX *ctx);
 int ssl_sock_prepare_all_ctx(struct bind_conf *bind_conf);
+int ssl_sock_prepare_bind_conf(struct bind_conf *bind_conf);
 int ssl_sock_prepare_srv_ctx(struct server *srv);
 void ssl_sock_free_srv_ctx(struct server *srv);
 void ssl_sock_free_all_ctx(struct bind_conf *bind_conf);