bhyve: only init MSI-X table if passthru device supports it
Some passthru devices only support MSI instead of MSI-X. For those
devices the initialization of MSI-X table will fail. Re-add the
check erroneously removed in f1442847c9404d4bc5f5524a0c3362dd39cb14f9.
MFC after: 3 days
X-MFC with: f1442847c9404d4bc5f5524a0c3362dd39cb14f9
PR: 260148
Reviewed by: manu, bz
Differential Revision: https://reviews.freebsd.org/D33728