As of now (git version 1.7.10.4) this is not supported yet.
You can read why the developers disagreed on how to implement. There were debates in 2009 an 2011 but no implementation so far as this seems to be tough.
It could be so easy (but it unfortunately is not):
git clone --continue
As one knows: Questions or comments for the Git community can be sent to the mailing list by using the email address git@vger.kernel.org. Bug reports should be sent to this mailing list. Just go ahead and ask there again :)
Git does not support resumable clones. That feature, it turns out, is
pretty tricky to implement properly. One workaround is to download a
bundle over http and then fetch the remaining bits and pieces with
git. But many repository admins do not provide bundles for you to
download. This service aims to fill that gap: give us the URL to a
repository and we'll create a bundle which you can download through
http. [ bundler.caurea.org ]
I tried this for qtmoko.git and looks works quite well. Another option is to ask upstream/github to implement "git bundle", there are howtos (How to use git-bundle for keeping development in sync?) for this as well.