IB/core: Add support for multicast loopback blocking

This patch also adds a creation flag for QPs,
IB_QP_CREATE_MULTICAST_BLOCK_LOOPBACK, which when set means that
multicast sends from the QP to a group that the QP is attached to will
not be looped back to the QP's receive queue.  This can be used to
save receive resources when a consumer does not want a local copy of
multicast traffic; for example IPoIB must waste CPU time throwing away
such local copies of multicast traffic.

This patch also adds a device capability flag that shows whether a
device supports this feature or not.
Signed-off-by: Ron Livne <ronli@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

include/rdma/ib_verbs.h

@@ -104,6 +104,7 @@ enum ib_device_cap_flags {
 	IB_DEVICE_UD_IP_CSUM		= (1<<18),
 	IB_DEVICE_UD_TSO		= (1<<19),
 	IB_DEVICE_MEM_MGT_EXTENSIONS	= (1<<21),
+	IB_DEVICE_BLOCK_MULTICAST_LOOPBACK = (1<<22),
 };
 
 enum ib_atomic_cap {
@@ -556,6 +557,7 @@ enum ib_qp_type {
 
 enum ib_qp_create_flags {
 	IB_QP_CREATE_IPOIB_UD_LSO		= 1 << 0,
+	IB_QP_CREATE_BLOCK_MULTICAST_LOOPBACK	= 1 << 1,
 };
 
 struct ib_qp_init_attr {