Run bpf_existence_test in mainline-postsubmit.

The TEST_MAPPING file already contains a mainline-postsubmit
stanza, but according to go/test-mapping-mainline-user-guide
this information also needs to be in AndroidTest.xml (or in
Android.bp, for tests that are not covered by an AndroidTest.xml
and where soong autogenerates the test config).

Test: m bpf_existence_test
Change-Id: I103f5fefbfefa6fd2b59ab6c209fbf1dceada4ba
2 files changed