Network: Implement ipv6/ipv4 default gateways on EthernetInterface

Currently ipv6/ipv4 default gateway properties on SystemConfiguration
interface which will be deprecated soon.
This commit is to add Default gateway properties implementation on
EthernetInterface.

Test by:
Set ipv4/v6 default gateway properties on ethernet interface.

Signed-off-by: Ravi Teja <raviteja28031990@gmail.com>
Change-Id: I30da81d7ccf9d568a60bfdd179331b4c0d86b149
6 files changed