[PATCH] Restore netstat -M functionality

[John Baldwin]

The primary purpose of this patch is to restore -M functionality of netstat so 
that it can pull information out of crash dumps.  Right now it just silently 
pulls stats from the running kernel for functions that use sysctl which is 
even worse than missing functionality: it lies.  It also fixes a subtle bug 
in the recent IPSEC changes which didn't renumber the N_xxx constants in the 
name list after removing a symbol which currently breaks all the IPSec stats.

The biggest things the patch does are:

- Add a global 'live' variable that is true if netstat is running against the
  live kernel and false if -M has been specified.
- Stop abusing the sysctl flag in the protocol tables to hold the protocol
  number.  Instead, the protocol is now its own field in the tables, and
  it is passed as a separate parameter to the PCB and stat routines rather
  than overloading the KVM offset parameter.
- Don't run PCB or stats functions who don't have a namelist offset if we are
  being run against a crash dump (!live).
- For the inet and unix PCB routines, we generate the same buffer from KVM
  that the sysctl usually generates complete with the header and trailer.
- Don't run bpf stats for !live (before it would just silently always run
  live).
- kread() no longer trashes memory when opening the buffer if there is an
  error on open and the passed in buffer is smaller than _POSIX2_LINE_MAX.
- The multicast routing code doesn't fallback to kvm on live kernels if
  the sysctl fails.  Keeping this made the code rather hairy, and netstat
  is already tied to the kernel ABI anyway (even when using sysctl's since
  things like xinpcb contain an inpcb) so any kernels this is run against
  that have the multicast routing stuff should have the sysctls.
- Don't try to dig around in the kernel linker in the netgraph PCB routine
  for core dumps.

One thing not done:
- sctp's PCB routine only works on live kernels, it looked rather complicated
  to generate all the same stuff via KVM.  Someone can always add it later if
  desired though.

Other stuff:
- Fix the ipsec removal bug where N_xxx for IPSEC stats weren't renumbered.
- Use sysctlbyname() everywhere rather than hardcoded mib values.

Patch is at http://www.FreeBSD.org/~jhb/patches/netstat_core_7.patch

A patch for 6.x is also available as netstat_core.patch

Barring any objections/feedback I will be committing this to CVS in a few days 
(subject to re@ approval of course).

-- 
John Baldwin