have margo-info diagnose if IPoIB is not configured for a potential Verbs interface

[carns]

See discussion in #235. Both ibstat and fi_info will report that Verbs interfaces are available regardless of whether they have IPoIB activated or not, but libfabric can only successfully activate them if IPoIB is running due to a dependency on it for rdmacm connection management (see https://ofiwg.github.io/libfabric/main/man/fi_verbs.7.html). This is difficult to diagnose.

We need to determine what programmatic API would be best to use for querying this so that we can map ibX IP interfaces to ports reported by libfabric correctly.