nfs-kernel-server: fix up init scripts and exports

nfs-kernel-server: fix up init scripts and exports

Add post-release patch to fix musl builds:
  250-fh_key_file-fix-missing-string.h-inclusion.patch

v3 init:
- Mirror upstream systemd service; use nfsdctl to manage the server
- Add /etc/nfs.conf to restrict to NFSv3 only:
  % cat /proc/fs/nfsd/versions
  +3 -4 -4.0 -4.1 -4.2

v4 init:
- Remove dead procd_append_param -F from nfsdcld instance
- Add respawn to nfsv4.exportd and rpc.idmapd; exclude nfsdcld as it
  daemonizes and would spawn duplicates under procd respawn
- Remove unused NFSDCLD_PID variable; nfsdcld writes no pidfile
- Add status_service() using pgrep; procd permanently misreports
  nfsdcld as stopped due to its daemonization behavior

exports:
- Supply unified /etc/exports covering both v3 and v4 syntax so the
  file survives switching between package variants

Signed-off-by: John Audia <redacted>