DHCP: parsing robustness fixes.
DHCP: parsing robustness fixes.

1. Check the length of the fixed-length portions of the packet.
2. Catch BufferUnderflowException while parsing options.

Change-Id: If907f49f02a04a4a3360f46a3192e94ab099af0e

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base