Fix AIBinder_linkToDeath not being called issue

The linked AIBinder_DeathRecipient will be automatically unlinked if the
binder is deleted. The binder needs to be retained throughout tests.

Bug: 172178636
Test: 1. run a test case to kill netd locally, do things like
         { system("netd=$(pidof netd); kill $netd"); }
      2. atest resolv_integration_test
      3. check if test fail and abort immediately on the test case.
Change-Id: Ic30d247d46d3b197ec9719b0db955495fc64435d