Merge changes Iddc971c7,If907f49f,I5505bd2c,I110b5800,I9aeb29c2, ...

* changes:
  DHCP: Don't write options longer than 255 bytes.
  DHCP: parsing robustness fixes.
  DHCP: Add a hidden setting to use the legacy DHCP client.
  DHCP: Add a Java DHCP client.
  Add a protectFromVpn method that takes a FileDescriptor
  DHCP: protocol changes.
  DHCP: glue code.
  DHCP: Ethernet/IP packet header changes.
  DHCP: Minor cleanups to the packet code.
  DHCP: Move the packet code to frameworks/base/services.
  DHCP: Add a native method for making a DHCP socket.
  DHCP: Add a superclass for DhcpStateMachine.
  Add two utility methods for IPv4 netmasks.