usnic: properly check src iface in route queries

rtnetlink doesn't check the source address when determining whether to
return route info for a query.  So we need to check that the OIF matches
the OIF of the source interface name.  Without this check, OMPI might
pair a local interface which does not have a route to a particular
remote interface.

Fixes Cisco bug CSCup55797.

Reviewed-by: Jeff Squyres <jsquyres@cisco.com>

cmr=v1.8.2:reviewer=ompi-rm1.8