net: usb: introduce usbnet_mii_ioctl helper function

net: usb: introduce usbnet_mii_ioctl helper function

Many USB network drivers use identical code to pass ioctl
requests on to the MII layer. Reduce code duplication by
refactoring this code into a helper function.

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev> (v1)
Reviewed-by: Andrew Lunn <andrew@lunn.ch> (v3)
Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20260203013517.26170-1-enelsonmoore@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>