Ubuntu: Add static routes per interface instead of a separate single file

[jbemmel]

Update: Modified to add static routes under each interface separately, such that the interface type is automatically correct

[ipspace]

This PR assumes the nexthop interfaces are all of the same type, which I believe is a safe assumption

Now that we support 'routing' module on Linux, this is no longer a safe assumption.

[ipspace]

No shortcuts. A Linux host could (theoretically) have static routes point to bond interfaces and native Ethernet interfaces.

[jbemmel]

No shortcuts. A Linux host could (theoretically) have static routes point to bond interfaces and native Ethernet interfaces.

ok, in that case I would propose to add the static routes in /etc/netplan/03-eth-[ifname].yaml instead of that separate single file