IB/core: Better checking of userspace values for receive flow steering

- Don't allow unsupported comp_mask values, user should check
    ibv_query_device to know which features are supported.
  - Add a check in ib_uverbs_create_flow() to verify the size passed
    from the user space.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

include/rdma/ib_verbs.h

@@ -1098,6 +1098,8 @@ enum ib_flow_spec_type {
 	IB_FLOW_SPEC_UDP	= 0x41
 };
 
+#define IB_FLOW_SPEC_SUPPORT_LAYERS 4
+
 /* Flow steering rule priority is set according to it's domain.
  * Lower domain value means higher priority.
  */