There's a deeper problem, which is that I'm not sure our network code
   guarantees any alignment at all of packets in mbufs.  mbuf(9) doesn't
   address alignment.  But it seems on sparc64 everything is naturally
   32-bit aligned, and 64-bit except for gif, or this would have blown up
   on other interfaces.


it's not upto mbuf(9) to do this.  it has no idea what alignment data
in packet data needs.  there's nothing to say that even given a well
aligned start address, that an aligned member won't be at an unaligned
offset, such as 4 bytes on a 2 byte boundary (this happens.)


.mrg.