Hostif Trap for route to interface (subnet route)

[rck-innovium]

Problem statement

There are cases where routes trap packets to CPU other than IP2ME routes. Defining a trap type allows the SAI application to:

1. decide the packet action (drop/trap)
2. rate limit by attaching a policer to the trap group
3. select the CPU queue via the trap group

Today, SAI has only defined a trap type for IP2ME packets (SAI_HOSTIF_TRAP_TYPE_IP2ME). The below scenarios need the route to point the packets to CPU but we do not have a trap type defined.

When an IP address and subnet, say 10.1.1.1/24 is on a RIF and a neighbor 10.1.1.2 is learnt, the following set of routes are needed:

1. 10.1.1.1/32 to CPU using SAI_HOSTIF_TRAP_TYPE_IP2ME,
2. 10.1.1.1/24 route : This route points to CPU when NOS wants hints to trigger ARP requests. Some NOS implementations can choose to blackhole this route. Today, SAI does not let the NOS control- whether this packets should be dropped or trapped, and more importantly when it is trapped it neither allows the user to rate-limit this traffic nor select the CPU queue.
3. 10.1.1.2/32 route: to the learnt neighbor

Related SAI constructs:

SAI has a user defined trap instead of a regular trap defined for neighbor.

/**
  * @brief Neighbor table traps
  *
  * Generated by neighbor table entry hit with action trap/log, or by neighbor table miss
  */
 SAI_HOSTIF_USER_DEFINED_TRAP_TYPE_NEIGHBOR

Why this is not sufficient? A user defined trap by definition can be attached to only the objects of that type. So a user defined trap of type SAI_HOSTIF_USER_DEFINED_TRAP_TYPE_NEIGHBOR can be attached only to a Neighbor object and not to a nexthop/route object.

What is required?

1. New Router trap type:

    /**
     * @brief Packets matching subnet routes with NH pointing to router interface
     * (default packet action is trap)
     */
    SAI_HOSTIF_TRAP_TYPE_IP2SUBNET = 0x00002015,

2. Fix the comments in SAI_HOSTIF_USER_DEFINED_TRAP_TYPE_NEIGHBOR

Generated by neighbor table entry hit with action trap/log, or by neighbor table miss for a router interface that has SAI_ROUTER_INTERFACE_ATTR_NEIGHBOR_MISS_PACKET_ACTION set to trap.