tmpfs - remove most mp->mnt_token cases, kqueue filterops are MPSAFE

tmpfs - remove most mp->mnt_token cases, kqueue filterops are MPSAFE

* tmpfs's kqueue filterops are MPSAFE, set appropriate flag.

* tmpfs's vnops frontend universally obtained the tmpfs mnt_token, but
  most of tmpfs's underlying code was already sub-locked by node.

  Remove most mnt_token use cases and make the portions that were not
  safe, safe.  This was primarily the directory lookup and scanning
  code and code to create, delete, and rename files.

* Should greatly improve tmpfs concurrency.