Exempt adb socket for hostside VpnTest

Vpn test would destroy socket. If adb run over network, adb
socket would be killed during Vpn test. Then, test stop due to
adb disconnect.

Bug: 119382723
Test: - build pass
      - run cts -m CtsHostsideNetworkTests -t com.android.cts.net.HostsideVpnTests

Change-Id: I91b4ab018a9e7fc73dcb7969e4a6520d6b27d629