hyperv/hn: Don't return error when setting media to autoselect

Setting media to autoselect would always return EOPNOTSUPP.
As autoselect is the only valid media, this change now returns
success instead.

PR: 264253
Reported by: Prakash Shiva <prakashs0234@gmail.com>
Reviewed by: Dexuan Cui <decui microsoft com>, whu
Approved by: whu
MFC after: 2 weeks