- cleanup SP refcnt issue.

- cleanup SP refcnt issue.
- share policy-on-socket for listening socket.
- don't copy policy-on-socket at all.  secpolicy no longer contain
  spidx, which saves a lot of memory.
- deep-copy pcb policy if it is an ipsec policy.  assign ID field to
  all SPD entries.  make it possible for racoon to grab SPD entry on
  pcb.
- fixed the order of searching SA table for packets.
- fixed to get a security association header.  a mode is always needed
  to compare them.
- fixed that the incorrect time was set to
  sadb_comb_{hard|soft}_usetime.
- disallow port spec for tunnel mode policy (as we don't reassemble).
- an user can define a policy-id.
- clear enc/auth key before freeing.
- fixed that the kernel crashed when key_spdacquire() was called
  because key_spdacquire() had been implemented imcopletely.
- preparation for 64bit sequence number.
- maintain ordered list of SA, based on SA id.
- cleanup secasvar management; refcnt is key.c responsibility;
  alloc/free is keydb.c responsibility.
- cleanup, avoid double-loop.
- use hash for spi-based lookup.
- mark persistent SP "persistent".
  XXX in theory refcnt should do the right thing, however, we have
  "spdflush" which would touch all SPs.  another solution would be to
  de-register persistent SPs from sptree.
- u_short -> u_int16_t
- reduce kernel stack usage by auto variable secasindex.
- clarify function name confusion.  ipsec_*_policy ->
  ipsec_*_pcbpolicy.
- avoid variable name confusion.
  (struct inpcbpolicy *)pcb_sp, spp (struct secpolicy **), sp (struct
  secpolicy *)
- count number of ipsec encapsulations on ipsec4_output, so that we
  can tell ip_output() how to handle the packet further.
- When the value of the ul_proto is ICMP or ICMPV6, the port field in
  "src" of the spidx specifies ICMP type, and the port field in "dst"
  of the spidx specifies ICMP code.
- avoid from applying IPsec transport mode to the packets when the
  kernel forwards the packets.

Tested by:	nork
Obtained from:	KAME