FR: Optionally wait for IP addresses

[mgreter]

I have the need to also wait until dhcp has assigned some ip addresses to the
interfaces before starting my firewall. Not sure if you want to include this, as
it needs the ip command from iproute2 pkg, but I figured I'd create a PR
anyway. Also included the bugfix from my other PR to avoid merge conflicts.

Thanks for consideration!

[williamh]

@mgreter Please rebase on master and remove the code for the other pull request. Also, in the future, please avoid putting code from multiple pull requests together.

Thanks,

William

[mgreter]

Done, rebased to latest master. And sorry, just kept it in to avoid merge conflicts!

[williamh]

@mgreter I like the concept, but I'm wondering if there is a more efficient way to do it that does not use head or grep. Also, you can test for the presence of the ip command with something like:

if [ -n "$(command -v ip)" ]; then
    # Now we know we have the ip command
fi

[mgreter]

It might be possible to use a construct like

if [[ $ipaddr == *"inet"* ]]; then

Will hopefully get around to test this upcoming weekend