I mean, under the scheme I outlined, the kernel is still going to do that by default. It's not that the NIC's driver is overridden or anything; the kernel would still be reading the receive buffer from this NIC and triggering per-packet handling — and thus triggering default kernel response-handling where applicable (and so responding to e.g. ICMP ARP messages correctly.)

The only thing that's different here, is that there are no active TCP or UDP listening sockets bound to the NIC — so when the kernel is scanning the receive buffer to decide what to do with packets, and it sees a TCP or UDP packet, it's going to look at its connection-state table for that protocol+interface, realize it's empty, and drop the packet for lack of consumer, rather than doing any further logic to it. (It'll bump the "dropped packets" counter, I suppose, but that's it.)

But, since there is a packet socket open against the NIC, then before it does anything with the packet, it's going to copy every packet it receives into that packet socket's (userspace-shared) receive-buffer mmap region.