Fix m_head handling in sis_encap so that the correct mbuf is always handed to BPF_MTAP.
Fix m_head handling in sis_encap so that the correct mbuf is always handed
to BPF_MTAP.

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