librdmacm: expand support for hints to rdma_getaddrinfo

librdmacm: expand support for hints to rdma_getaddrinfo

If a user passes in hints into rdma_getaddrinfo, they can
specify resolved source and destination addresses.  In this
case, there's no need for the user to specify the node or
service parameters.  This differs from getaddrinfo, which
indicates that either node or service must be provided, but
is useful if rdma_getaddrinfo is being used to obtain
routing data.

Supporting this option allows the librdmacm to call
rdma_getaddrinfo internally from rdma_resolve_route when IB ACM
is enabled.

In addition to specifying the source and destination addresses
as part of the hints, a user could instead specify partial
routing data and rdma_getaddrinfo can resolve the full route.

This helps to support MPI applications that exchange endpoint
data, such as LIDs, out of band, but require SL data from the
SA to avoid potential deadlock conditions.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>