drm - Fix improper M_NOWAIT usage

* Remove numerous mis-uses of M_NOWAIT, replacing with M_WAITOK | M_NULLOK.
mountd - Look up addresses before using getnetbyname()

- Lookup '-network' and '-mask' addresses numerically before trying
  getnetbyname()
- This avoids silly DNS queries.

Taken from: FreeBSD SVN 75861
kernel - Fix race in recent callout work

* CALLOUT_ARMED can only be cleared if the callout is not PENDING and also
  if there are no IPIs pending.  The last bit wasn't being checked properly,
  potentially leading to MP races.
nfs - Remove unused kerberos code [Userland]

- This commit removes unused kerberos code from mount_nfs(8) and
  mountd(8).
- After a bit of research, apparently the code never worked on FreeBSD
  since it was imported around 1995

Partially taken from: FreeBSD SVN 83653