opal/common/ofi: refactor NIC selection logic

This patch refactors the OFI NIC selection logic. It foremost improves
the NIC search algorithm. Instead of searching for the closest NICs on
the system, this patch directly compares the distances of the given
providers and selects the nearest NIC.

This change also makes it explicit that if the process is unbound, or
the distance cannot be reliably calculated, a provider will be selected
in round-robin fashion.

Signed-off-by: Wenduo Wang <[email protected]>