network: mark container/VM/namespace networks as not required for online + disable DHCP lease persistency

These networks are not connections to upstream routers, but where we are
ourselves are the upstream router, hence it doesn't make too much sense
to require them to be up as default to determine if we are "online",
because they lead "in the wrong direction".

Also, disable DHCP lease persistency for these networks, since
container/VM/namespaces are generally shortlived, and typically have no
persistent identity. Moreover, the IP range we assign each VM/container
connection is just too small to permit persistency, as otherwise we'll
run out of leases way too quickly if VM/containers are restarted a bunch of
times with different MAC addresses (which I ran into).

I think these are better defaults, but of course these are only
defaults.

network/80-container-vb.network

@@ -14,6 +14,9 @@
 Kind=veth
 Name=vb-*
 
+[Link]
+RequiredForOnline=no
+
 [Network]
 KeepMaster=yes
 LinkLocalAddressing=no

network/80-container-ve.network

@@ -14,6 +14,9 @@
 Kind=veth
 Name=ve-*
 
+[Link]
+RequiredForOnline=no
+
 [Network]
 # Default to using a /28 prefix, giving up to 13 addresses per container.
 Address=0.0.0.0/28
@@ -24,3 +27,6 @@ LLDP=yes
 EmitLLDP=customer-bridge
 IPv6AcceptRA=no
 IPv6SendRA=yes
+
+[DHCPServer]
+PersistLeases=no

network/80-container-vz.network

@@ -13,6 +13,9 @@
 Kind=bridge
 Name=vz-*
 
+[Link]
+RequiredForOnline=no
+
 [Network]
 # Default to using a /24 prefix, giving up to 253 addresses per virtual network.
 Address=0.0.0.0/24
@@ -23,3 +26,6 @@ LLDP=yes
 EmitLLDP=customer-bridge
 IPv6AcceptRA=no
 IPv6SendRA=yes
+
+[DHCPServer]
+PersistLeases=no

network/80-namespace-ns.network

@@ -14,6 +14,9 @@
 Kind=veth
 Name=ns-*
 
+[Link]
+RequiredForOnline=no
+
 [Network]
 # Default to using a /28 prefix, giving up to 13 addresses per namespace
 Address=0.0.0.0/28
@@ -24,3 +27,6 @@ LLDP=yes
 EmitLLDP=customer-bridge
 IPv6AcceptRA=no
 IPv6SendRA=yes
+
+[DHCPServer]
+PersistLeases=no

network/80-vm-vt.network

@@ -13,6 +13,9 @@
 Kind=tun
 Name=vt-*
 
+[Link]
+RequiredForOnline=no
+
 [Network]
 # Default to using a /28 prefix, giving up to 13 addresses per VM.
 Address=0.0.0.0/28
@@ -23,3 +26,6 @@ LLDP=yes
 EmitLLDP=customer-bridge
 IPv6AcceptRA=no
 IPv6SendRA=yes
+
+[DHCPServer]
+PersistLeases=no