gen_makefile: update URL code for netfilter urls

* libgtnpnl is now developed at gerrit.osmocom.org
* use https:// instead of git:// for libnftnl, nftables
* read the urls from a new all.urls file
* don't set a push URL pointing to gerrit for projects that have
  different URLs

Change-Id: I5522c9fcc594d296c581ba59c0beb4882e2d976e
2 files changed