add extlinux to core now that's it's no longer in stage1

the rationale behind removing it from stage1 was
- extlinux is of little use on non x86 hw
- it can even be of little use when the x86 expects uefi
- stage1 originally meant a completely bootable rootfs
  including kernel. but the kernel has been removed a long time
  ago from stage1, as the config only works for x86 archs anyway.
  as of now its meaning is "basic standalone chroot that's equipped
  with everything needed to build the kernel and other packages"
add socat package
go only has a https download url, so it should depend on wget