[RFCLAT#9] refactor getinterface_ip() to stop using libnl am: 208b2a1a0c am: 62890f37d3 am: 9b0bb6bde7

Original change: https://android-review.googlesource.com/c/platform/external/android-clat/+/1908656

Change-Id: Ibe161eab4c2f3e96a01b60021625991a8879d5f5