Systemd mount.nfs fails: Network is unreachable on Ubuntu 16.04

I've setup an NFS mount in the /etc/fstab file of an Ubuntu 16.04.6 machine.
The NFS fails at every boot, I noticed that when the Unity Greeter comes up the network icon on the top right of the screen shows the network as disconnected, and after 5 seconds it starts the connection process and succeeds. At this point, if I login and run mount -a as a superuser, it works just fine.I have tried a bunch of options to force systemd to wait for network, but nothing works...How do I force NetworkManager to connect before I get to the greeter?I don't mind the extra boot time delay.