nwfilter: let qemu's after-migration packet pass

nwfilter: let qemu's after-migration packet pass

Qemu currently sends an Ethernet packet with protocol id 0x835 once a VM
was successfully migrated. The content of the packet looks like a
gratuitous RARP, just with the wrong protocol ID, which should be
0x8035. I wrote some filters to let either one of the packets pass and
am adapting the clean-traffic sample filter to use it. I am also
doing some changes on the existing ARP filter which was lacking a
test for source MAC address.