Use the httpd-2.4 API function ap_get_conn_socket to set the socket timeout. This has been wrong since 2.4, and the socket timeout hasn't been set correctly. mod_ftp segfaults after httpd change r1839997 because setting the timeout clobbers the filter context.
Introduce the HOST command (and XWEL command for diagnostics), and support for TLS-SNI provided hostname via an implicit HOST invocation. Corrects headers and fields to ensure the host names are initialized at the appropriate times, and that the orig_server maps to the correct host. This is known to work correctly with the latest Filezilla (uses SNI by default), for both Explicit and Implicit SSL connections on httpd-2.2, but the SSL logic is known to be broken for the data channel on httpd-2.4 (likely not a regression).