Restructuring inpcb/in6pcb

[Ryota Ozaki <ozaki.ryota%gmail.com@localhost>]

Hi,

Data structures of network protocol control blocks (PCBs)
(struct inpcb, in6pcb and inpcb_hdr) are not organized well.
Users of the data structures have to handle them separately
and thus the code becomes duplicated and cluttered.

The proposal restructures the data structures, which eliminates
duplicate and cluttered code and makes further changes easy.

A typical cleanup by the change looks like this:

-       if (tp->t_inpcb)
-               so = tp->t_inpcb->inp_socket;
-#ifdef INET6
-       else if (tp->t_in6pcb)
-               so = tp->t_in6pcb->in6p_socket;
-#endif
+       so = tp->t_inpcb->inp_socket;

Also some duplicated functions for IPv4 and IPv6 are integrated:
tcp6_notify, tcp6_quench, etc.

The change consists of two parts.  The first half of the series of
commits tries to integrate all the data structures into one structure
(struct inpcb).  The commits cleans up ugly code like above.
However, because the structure includes both IPv4 and IPv6 stuff,
the data size for IPv4 increases by 40 bytes (from 248 to 288).

The second half of the series of commits addresses the increasement
of the data size by separating the data structure again while keeping
the code simple.  By the change, struct inpcb has only common data
and newly introduced data structures, struct in4pcb and struct in6pcb
inherited from struct inpcb, have dedicated data for each protocol.
Even after the separation, users don't need to recognize the separation
and just need to use some macros to access dedicated data.
For example, inp->inp_laddr, which represents the local IPv4 address,
is now accessed through in4p_laddr(inp).  Using these macros adds
some code complexity, but this is a trade-off between data size and
code complexity.

The diffs are here:
- https://www.netbsd.org/~ozaki-r/restructure-inpcb-1.patch
- https://www.netbsd.org/~ozaki-r/restructure-inpcb-2.patch

Also, you can see individual commits at github:
  https://github.com/ozaki-r/netbsd-src/commits/restructure-inpcb


We can adopt either of the whole changes or only changes of the first half.
Which should we choose? Smaller data size or simpler code?

By the way, I think the changes should be committed (if permitted)
after branching netbsd-10.  When will the netbsd-10 branch come?
If it doesn't come soon, is it ok to commit the changes before branching?

Thanks,
   ozaki-r