Fix null DadProxy failure in R Tethering unit test

Tethering unit test would verify the interfaction between DadProxy and
IpServer. Since DadProxy only available in S+, the test would fail if it
build with R sdk.

Bug: 171936270
Test: atest TetheringTests in both R and S
Change-Id: Ia73d4aa59d01400d1ccfd3fdc1b721e269cae952
1 file changed
tree: 7064181a344b7df7c7073308068f77f0f0629507
  1. Tethering/