Add shims to get and set the NAT64 prefix in LinkProperties.

Bug: 153694684
Test: m NetworkStack NetworkStackNext
Merged-In: I934fed7a0a8921d3dce7584b5f1b74a0ad67f14a
Change-Id: I934fed7a0a8921d3dce7584b5f1b74a0ad67f14a
3 files changed