VPN: add VpnBuilder as the public API of user space VPN.
VPN: add VpnBuilder as the public API of user space VPN.

Change-Id: I5d30cf592bead315509038632647c88de5060e50

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