[RFC] swap event handling fixes

[Jesse Barnes]

I obviously failed to count the swap event structure size after adding
and removing fields a few times, and didn't even account for padding.  The
end result is that clients today won't receive the sbc_lo field at all,
and so will likely stuff junk into that field on the client side (or
zero at best).

This patchset fixes up the structure definitions, bumps the proto
levels, and adds server and client handling code for it all.  It should
be forward and backward compatible, but as always review and testing
appreciated.

I think the event_type checking on the client side still needs work;
the field is split now so I need to check the right one on old servers.
I'll also add swap support for the new requests in case people ever want
to run this stuff between big and little endian machines.

Thanks,
Jesse