pxeboot is very slow on servers sending gratuitous ARP probably caused by commit r317887

[Andreas Longwitz]

After update from FreeBSD V10 Stable to FreeBSD 12 Stable (r360998) the
load of a kernel in pxeboot via NFS is very slow because my server sends
gratuitous ARP packets every 2 seconds.

pxeboot from 11.1 REL (r321354) is ok.
pxeboot from 11.2 REL (r335563) is very slow too.

For every ARP the server sends the kernel download in pxeboot stops for
two seconds and then continues after timeout of 2 seconds (because of
work done in r329264).

I am quite sure that commit r317887 changed things for ARP packets. pxe
does not use udpsend/udpreceive anymore and the new code with undi
interface does nothing to filter the ARP's.


Andreas Longwitz