systemd: Only start smb when network interfaces are up

systemd: Only start smb when network interfaces are up

For smb, if the smb.conf contains explicit bindings to the network
interfaces, the service must wait till network interfaces are up,
otherwise the service won't be operational.

The 0e571054a61e commit and the BZ 13184 have fixed this for nmb and
samba, so do exactly the same here, for smb.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13559

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Fri Aug  3 17:28:52 CEST 2018 on sn-devel-144