network: fix calculation of DHCP range for /16 networks

When generating DHCP ranges for /16 networks, we are right at the limits
of what libvirt supports. We try to limit the number of hosts to at most
2^16-1 in case of large subnets.

However, the check was incorrect, as for a /16 network we would define the end
range as being .255.255, i.e. the broadcast address. So when we have a /16
network, we are still in the default case of having to decrement the "last" IP
by one.

cmd/network_add.go

@@ -144,7 +144,7 @@ func buildNetworkDHCP(ip net.IP, n *net.IPNet, dhcpMAC string, dhcpID uint, dhcp
 
 	prefix, hostBits := n.Mask.Size()
 	// libvirt does not support more than 2^16-1 hosts in the dhcp range
-	if hostBits-prefix >= 16 {
+	if hostBits-prefix > 16 {
 		end, _ = cidr.Host(n, 65535)
 	} else {
 		end = cidr.Dec(end)