CA-99179: Add other_config param for disabling default gateway advertising on host-internal-management network 

Patches XAPI to allow clients to stop XAPI from generating a udhcpd 
config file that includes advertising dom0's IP as the default gateway 
for the network.

When using the host internal management network with Windows VMs
the network adapter will be allocated a high metric based on its speed,
and so traffic to unkown destinations may be routed via Dom0.