Set single Default Gateway on instance inspite of having attached to mulitple networks.

Issue

• Instance is attached to two or more provider networks but only one default gateway is required.

  # route -n
  Kernel IP routing table
  Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
  0.0.0.0         192.168.123.254 0.0.0.0         UG    100    0        0 eth0      #gateway1
  0.0.0.0         192.168.124.254 0.0.0.0         UG    101    0        0 eth1      #gateway2
  XXX.254.169.254 192.168.123.254 255.255.255.255 UGH   100    0        0 eth0
  192.168.123.0   0.0.0.0         255.255.255.0   U     100    0        0 eth0
  192.168.124.0   0.0.0.0         255.255.255.0   U     101    0        0 eth1
  

• Need only one default gateway.

  # route -n
  Kernel IP routing table
  Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
  0.0.0.0         192.168.123.254 0.0.0.0         UG    100    0        0 eth0    # only gateway1 is required as default.
  XXX.254.169.254 192.168.123.254 255.255.255.255 UGH   100    0        0 eth0
  192.168.123.0   0.0.0.0         255.255.255.0   U     100    0        0 eth0
  192.168.124.0   0.0.0.0         255.255.255.0   U     101    0        0 eth1