- suggest the setup-alpine command in motd

- fix sysctl location and contents
  put sysctl to /etc/sysctl.d with 00 prefix so later sysctl.d files can
  override it if needed.

  also remove ip_forward, it default to zero in kernel, and is controlled
  by iptables init.d or quagga.

- mkmntdirs: add missing header
  string.h is needed for strcmp definition

- profile: remove LANG. ref #4428