IPoIB: Specify Traffic Class with path record queries for QoS support

To support QoS within and between subnets, modify IPoIB to request
specific Traffic Class values with path record queries, using
the value associated with the IPoIB broadcast group.

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

[ See some comments I made on this at v1 and v2 of the posts
  <http://lists.openfabrics.org/pipermail/general/2007-August/039275.html>
  <http://lists.openfabrics.org/pipermail/general/2007-September/040312.html

> ]

Reviewed-by: Or Gerlitz <ogerlitz@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>