net/mlx5e: Avoid WARN_ON when configuring MQPRIO with HTB offload enabled

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net/mlx5e: Avoid WARN_ON when configuring MQPRIO with HTB offload enabled When attempting to enable MQPRIO while HTB offload is already configured, the driver currently returns `-EINVAL` and triggers a `WARN_ON`, leading to an unnecessary call trace. Update the code to handle this case more gracefully by returning `-EOPNOTSUPP` instead, while also providing a helpful user message.

References

• https://git.kernel.org/stable/c/090c0ba179eaf7b670e720aa054533756a43d565
• https://git.kernel.org/stable/c/b82e496531c571caf8a2ef247f51c160bab2162e
• https://git.kernel.org/stable/c/9e2bac6835f73895598df5a3a125a19497fad46b
• https://git.kernel.org/stable/c/689805dcc474c2accb5cffbbcea1c06ee4a54570