librdmacm: Support using GIDs with rdma_getaddrinfo

librdmacm: Support using GIDs with rdma_getaddrinfo

Allow the user to specify a GID as the node parameter into
rdma_getaddrinfo.

To distinguish between the node being an IPv6 address or a GID,
we add a new flag, RAI_FAMILY, which can be set as part of the
hints to rdma_getaddrinfo.  When set, this flag indicates that the
value of ai_family in the hints should be used when interpretting
the node parameter.

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