IB/usnic: Port over usnic_ib_qp_grp.[hc] to new usnic_fwd.h

This patch ports usnic_ib_qp_grp.[hc] to the new interface
of usnic_fwd.h.

Signed-off-by: Upinder Malhi <umalhi@cisco.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>