kern_sysctl.c locking

[Joerg Sonnenberger]

Hi all,
the patch ftp://82.144.62.50/kern_sysctl.c.diff adds proper locking
to the sysctl code to make it SMP safe. Additionally I made the printf
for unregistering an OID_AUTO field a panic, which simplifies the code
and is IMO a real error condition.

Please test this code, esp. on SMP, TTC is 3 days.

Joerg