Add netlink submodule

This contains various operations that can replace the use of
shelling out to "ip".
Use netlink directly instead of /bin/ip in Sysinit

The sysinit code only uses /bin/ip to set a default gateway. This
is pretty easy to do via netlink directly, so we can avoid
the ip dependency.
network: Stop shelling out to /sbin/ip

We have our own netlink version of all the required calls now, so
we can just skip the /sbin/ip dependency.
Add a network test

This just tries pinging first 127.0.0.1 and then 8.8.8.8.

We can't ping via a dns name, because libresolv.so is missing
from the test image, so dns resolving doesn't work.
Move ListOps to utils submodule

This will be needed for later use in docker-init without a docker
dependency
Move SysInit to a submodule

This allows docker-init to not import the main docker
module, which means it won't e.g. pick up any sqlite
dependencies.