L3 router drops never increment relevant counters #404

Router4/Router6 (and their multicast cousins) set a drop reason on lookup or TTL failure, but need to delegate packet handling to the switch zone via the CPU port. So they cannot set meta.dropped -- we need to transform the packet and keep it moving. However, all of our drop counters in the ingress pipeline only touch drop statistics if we're actually dropping the packet, rather than transforming it:

We need to perform the counter operations on meta.drop_reason != 0, as egress does. We could also possibly replace meta.dropped with direct use of ig_dprsr_md.drop_ctl if needed.