vlan and bpf

[Greg Troxel <gdt%lexort.com@localhost>]

I am using vlans (on wm0 and vlan0), and when I run tcpdump on the
parent, I see the packets that are on the vlan.

This is causing trouble because dhcpd is seeing them.

I think it's a bug; the packet is on wm0 with a vlan tag, but it is not
on wm0 in the normal sense.  It shows up when tcpdumping on vlan0, which
is correct.  So I think packets with a vlan tag not for this interface
should not hit bpf_mtap.

This patch has not even been compiled, and I know it misses the
non-percpuq case, but I'm including it to say more clearly what I am
thinking.

--- if.c.~1.457.2.4.~   2020-09-01 19:56:43.824457852 -0400
+++ if.c        2023-12-15 12:10:09.503560965 -0500
@@ -818,7 +818,8 @@ if_percpuq_softint(void *arg)

        while ((m = if_percpuq_dequeue(ipq)) != NULL) {
                ifp->if_ipackets++;
-               bpf_mtap(ifp, m, BPF_D_IN);
+               if (!vlan_has_tag(m))
+                       bpf_mtap(ifp, m, BPF_D_IN);

                ifp->_if_input(ifp, m);
        }