net: libwx: restrict change user-set RSS configuration

Enable/disable SR-IOV will change the number of rings, thereby changing
the RSS configuration that the user has set.

So reject these attempts if netif_is_rxfh_configured() returns true. And
remind the user to reset the RSS configuration.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Link: https://patch.msgid.link/20250926023843.34340-5-jiawenwu@trustnetic.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>