Fix libnativeloader_test

Just before the test is enabled, the neuralnetwork namespace was added
by https://android-review.googlesource.com/c/platform/system/core/+/1014637.
This is breaking the libnativeloader_test.

Fix the test by adding the code for the new namespace.

Bug: 138304345
Test: libnativeloader_test on aosp_cf_x86_phone
Change-Id: Ifa762e395a3b9b5debdbcfcbcb395eeda3a1b2a4