The ethernet header size is not word aligned. Therefore the IP packet and so
on won't be align. On some architecture (such as ARM) unaligned access may
be slower and/or not supported. Therefore we might reveice an alignement
fault. To avoid this case, we need to pull-up the data of ETHER_ALIGN bytes.
I'm not sure how this patch will impact x86, we need to do some benchmarking
without and with it.
Furthermore, I don't know if m_copyup is the rigth function to use here. Can
any expert to the network stack can tell me if there is a better solution?