zebra: notify nht client about protocol type change

[enkechen-panw]

The protocol type is of interest to NHT clients. Comparea the field for changes.

[donaldsharp]

Can you point me to a place that this matters in a protocol? I'd like to understand this requirement change. Additionally this would clearly change behavior for both pim and bgpd in that they both assume that nht is only informing them of changes in what nexthops are being used. They both do a lot of work that could conceivably be completely unnecessary and I would not want changes in behavior here not be accounted for in the upper level protocols as well.

[enkechen-panw]

@donaldsharp Here they are:

bgp_nexthop_update()
  bgp_process_nexthop_update()
           if (import_check && (nhr->type == ZEBRA_ROUTE_BGP ||
                             !prefix_same(&bnc->prefix, &nhr->prefix))) {
                SET_FLAG(bnc->change_flags, BGP_NEXTHOP_CHANGED);
                UNSET_FLAG(bnc->flags, BGP_NEXTHOP_VALID);

static_zebra_nexthop_update():

        if (nhr->type == ZEBRA_ROUTE_CONNECT) {
                if (static_nexthop_is_local(vrf->vrf_id, matched,
                                            nhr->prefix.family))
                        nhr->nexthop_num = 0;
        }