Add a comment explaining that we initialize the 'a' buffer for zero-copy to the store buffer position on the BPF descriptor, and the 'b' buffer as the free buffer in order to fill them in the order documented in bpf(4).
Add a comment explaining that we initialize the 'a' buffer for
zero-copy to the store buffer position on the BPF descriptor,
and the 'b' buffer as the free buffer in order to fill them in
the order documented in bpf(4).

MFC after:	4 months
Suggested by:	csjp

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase