net-firewall/firewalld: version bump to 0.73

net-firewall/firewalld: version bump to 0.73

Also fix dependencies and add USE=+nftables

 - The iptables (ip6tables, ebtables, ipset) backend for firewalld is
   nowadays entirely optional. Thus add a use flags to control which
   backend is used and configured at compile time.

   This allows to drop iptables from the set of installed packages
   alltogether.

 - In case both, xtables and nftables are set also depend on
   nftables[xtables].

 - install locales

Closes: https://bugs.gentoo.org/670932
Closes: https://bugs.gentoo.org/709856
Bug: https://bugs.gentoo.org/703322
Package-Manager: Portage-2.3.94, Repoman-2.3.21
Signed-off-by: Matthias Maier <tamiko@gentoo.org>