considering cache line hits and misses.  Put the lock and hash list
glue into the first cache line, put inp_refcount inp_flags inp_socket
into the second cache line.

including inp_route inp_lle inp_gencnt.  When inp_route and inp_lle were
introduced, they were added below inp_zero_size, resulting on not being
cleared after free/alloc.  This definitely was a source of bugs with route
caching.  Could be that r315956 has just fixed one of them.
The inp_gencnt is reinitialized on every alloc, so it is safe to clear it.