The Berkeley Packet Filter (bpf) driver needs to be enabled before running programs that utilize it. Add this to your kernel config file and build a new kernel:
pseudo-device bpfilter # Berkeley Packet Filter
Secondly, after rebooting you will have to create the device
node. This can be accomplished by a change to the /dev
directory, followed by the execution of:
# sh MAKEDEV bpf0
Please see the handbook's entry on device nodes for more information on creating devices.