[tls] Use intf_insert() to add TLS to an interface

Restructure the use of add_tls() to insert a TLS filter onto an
existing interface.  This allows for the possibility of using
add_tls() to start TLS on an existing connection (as used in several
protocols which will negotiate the choice to use TLS before the
ClientHello is sent).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/http.h

@@ -45,11 +45,9 @@ struct http_scheme {
 	 *
 	 * @v xfer		Data transfer interface
 	 * @v name		Host name
-	 * @v next		Next interface
 	 * @ret rc		Return status code
 	 */
-	int ( * filter ) ( struct interface *xfer, const char *name,
-			   struct interface **next );
+	int ( * filter ) ( struct interface *xfer, const char *name );
 };
 
 /** HTTP scheme table */

src/include/ipxe/tls.h

@@ -378,7 +378,6 @@ struct tls_connection {
 /** RX I/O buffer alignment */
 #define TLS_RX_ALIGN 16
 
-extern int add_tls ( struct interface *xfer, const char *name,
-		     struct interface **next );
+extern int add_tls ( struct interface *xfer, const char *name );
 
 #endif /* _IPXE_TLS_H */