Use the format:

  apkovl=http://<server>/path/host.apkovl.tar.gz

when using apkovl from http.

instead, check if OVL_DEV is an URI

Use ALPINE_DEV_FS to detect nfs instead of adding an additional
variable

This supports network boot over NFS providing the correct kernel modules and
udhcpc hook script are incorporated to the initrd (tweak mkinitfs config).

The init script can now obtain an IP using udhcpc if you specify ip=dhcp.
This replaces kernel-level DHCP.

Downloading an ovl via http now works also. Use ovl_dev=http://...
You can now specify a repository at a different location than at the alpine_dev.
Use alpine_repo=http://nl.alpinelinux.org/...
By default, or if alpine_repo=auto, a repository will be searched for
on the alpine_dev, as usual. alpine_dev can now be an NFS share using
  alpine_dev=nfs:IP:EXPORT
The NFS share is currently necessarily mounted using -o nolock.

To boot over PXE you might use
  ip=dhcp alpine_dev=nfs:1.2.3.4:/... ovl_dev=http://.../foo.apkovl.tar.gz

You can use {MAC} and {UUID} in opk_dev. They will be substituted.
Ensure you put the value of opk_dev in quotes, e.g.
  opk_dev="http://.../?mac={MAC}"

Example file and driver list for PXE boot:
  kernel/drivers/net/ethernet/*
  kernel/net/packet/af_packet.ko
  kernel/fs/nfs/*
  kernel/fs/lockd/*
  kernel/net/sunrpc/*
  usr/share/udhcpc/default.script