devlink: let driver opt out of automatic phys_port_name generation

Currently when adding devlink port, phys_port_name is automatically
generated within devlink port initialization flow. As a result adding
devlink port support to driver may result in forced changes of interface
names, which breaks already existing network configs.

This is an expected behavior but in some scenarios it would not be
preferable to provide such limitation for legacy driver not being able to
keep 'pre-devlink' interface name.

Add flag no_phys_port_name to devlink_port_attrs struct which indicates
if devlink should not alter name of interface.

Suggested-by: Jiri Pirko <[e-mail]>
Link: https://lore.kernel.org/all/nbwrfnjhvrcduqzjl4a2jafnvvud6qsbxlvxaxilnryglf4j7r@btuqrimnfuly/
Signed-off-by: Jedrzej Jagielski <[e-mail]>
Signed-off-by: Tony Nguyen <[e-mail]>

include/net/devlink.h

···
  * @flavour: flavour of the port
  * @split: indicates if this is split port
  * @splittable: indicates if the port can be split.
+ * @no_phys_port_name: skip automatic phys_port_name generation; for
+ *		       compatibility only, newly added driver/port instance
+ *		       should never set this.
  * @lanes: maximum number of lanes the port supports. 0 value is not passed to netlink.
  * @switch_id: if the port is part of switch, this is buffer with ID, otherwise this is NULL
  * @phys: physical port attributes
···
  */
 struct devlink_port_attrs {
 	u8 split:1,
-	   splittable:1;
+	   splittable:1,
+	   no_phys_port_name:1;
 	u32 lanes;
 	enum devlink_port_flavour flavour;
 	struct netdev_phys_item_id switch_id;

net/devlink/port.c

···
 	struct devlink_port_attrs *attrs = &devlink_port->attrs;
 	int n = 0;
 
-	if (!devlink_port->attrs_set)
+	if (!devlink_port->attrs_set || devlink_port->attrs.no_phys_port_name)
 		return -EOPNOTSUPP;
 
 	switch (attrs->flavour) {