This patch uses the Berkeley Packet Filter (BPF) feature so that the
kernel only hands packets to a vblade process when they match its
shelf and slot address.

Without this patch, each vblade process would be woken up only to
discard an AoE packet destined for a different vblade running on the
same host.

This patch currently introduces a build dependency on the headers from
libpcap.  Usually a Linux distribution will include these headers in a
package with a name something like "libpcap-dev".