cxgbe(4): Get Linux cxgb4vf working in bhyve VMs with VFs passed
through.

cxgb4vf doesn't own the buffer size list but still expects the first two
entries to be 4K and some power of 2 respectively. The BSD cxgbe
doesn't care where its preferred buffer sizes are as long as they're in
the list somewhere, so just move its entries towards the end as a
workaround.

MFC after: 1 month
Sponsored by: Chelsio Communicatons