kauth(9) PAGs for Arla

things to touch

nnpfs_install_syscalls()
- replace what regular function?
  - sys_setgroups()? -- probably only called from userland
  - kauth_cred_setgroups()? -- probably called from within kernel, probably mostly from sys_setgroups()
nnpfs_setgroups() -- replacement for sys_setgroups()
- figure out the kauth-itization of this
sys_nnpfspioctl()
store_pag()