API to detect which network interfaces support wake-on-lan

Add a new method in LinkProperties, isWakeOnLanEnabled() which returns
true if network interface is defined in config_wakeonlan_enabled_interfaces
string-array (config.xml)

Bug: 132705025
Test: atest LinkPropertiesTest & atest ConnectivityServiceTest
Change-Id: I3f7803aafd2f8eaf8aa18419b21339e15d4b7a0b