kernel - Move MP lock inward, plus misc other stuff

kernel - Move MP lock inward, plus misc other stuff

* Remove the MPSAFE flag from the syscalls.master file.  All system calls
  are now called without the MP lock held and will acquire the MP lock if
  necessary.

* Shift the MP lock inward.  Try to leave most copyin/copyout operations
  outside the MP lock.  Reorder some of the copyouts in the linux emulation
  code to suit.

  Kernel resource operations are MP safe.

  Process ucred access is now outside the MP lock but not quite MP safe
  yet (will be fixed in a followup).

* Remove unnecessary KKASSERT(p) calls left over from the time before
  system calls where prefixed with sys_*

* Fix a bunch of cases in the linux emulation code when setting groups
  where the ngrp range check is incorrect.