Revert "usb: gadget: u_ether: Add auto-cleanup helper for freeing net_device"

This reverts commit 0c09811.

This commit is being reverted as part of a series-wide revert.

By deferring the net_device allocation to the bind() phase, a single
function instance will spawn multiple network devices if it is symlinked
to multiple USB configurations.

This causes regressions for userspace tools (like the postmarketOS DHCP
daemon) that rely on reading the interface name (e.g., "usb0") from
configfs. Currently, configfs returns the template "usb%d", causing the
userspace network setup to fail.

Crucially, because this patch breaks the 1:1 mapping between the
function instance and the network device, this naming issue cannot
simply be patched. Configfs only exposes a single 'ifname' attribute per
instance, making it impossible to accurately report the actual interface
name when multiple underlying network devices can exist for that single
instance.

All configurations tied to the same function instance are meant to share
a single network device. Revert this change to restore the 1:1 mapping
by allocating the network device at the instance level (alloc_inst).

Reported-by: David Heidelberg <david@ixit.cz>
Closes: https://lore.kernel.org/linux-usb/70b558ea-a12e-4170-9b8e-c951131249af@ixit.cz/
Fixes: 56a512a ("usb: gadget: f_ncm: align net_device lifecycle with bind/unbind")
Cc: stable <stable@kernel.org>
Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://patch.msgid.link/20260309-f-ncm-revert-v2-4-ea2afbc7d9b2@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Kuen-Han Tsai

drivers/usb/gadget/function/u_ether.c

@@ -1126,21 +1126,6 @@ void gether_cleanup(struct eth_dev *dev)
 }
 EXPORT_SYMBOL_GPL(gether_cleanup);
 
-void gether_unregister_free_netdev(struct net_device *net)
-{
-	if (!net)
-		return;
-
-	struct eth_dev *dev = netdev_priv(net);
-
-	if (net->reg_state == NETREG_REGISTERED) {
-		unregister_netdev(net);
-		flush_work(&dev->work);
-	}
-	free_netdev(net);
-}
-EXPORT_SYMBOL_GPL(gether_unregister_free_netdev);
-
 /**
  * gether_connect - notify network layer that USB link is active
  * @link: the USB link, set up with endpoints, descriptors matching

drivers/usb/gadget/function/u_ether.h

@@ -283,8 +283,6 @@ int gether_get_ifname(struct net_device *net, char *name, int len);
 int gether_set_ifname(struct net_device *net, const char *name, int len);
 
 void gether_cleanup(struct eth_dev *dev);
-void gether_unregister_free_netdev(struct net_device *net);
-DEFINE_FREE(free_gether_netdev, struct net_device *, gether_unregister_free_netdev(_T));
 
 void gether_setup_opts_default(struct gether_opts *opts, const char *name);
 void gether_apply_opts(struct net_device *net, struct gether_opts *opts);