get selinux context on add call arrival. interfaceChain may take too long and allow for the PID to become invalidated. Bug: 68217907 Test: hidl's run_all_device_tests, boot + camera/YT sanity Merged-In: Ie69d92f9006d10e7e3e4871f5760823291ed8e1f Change-Id: Ie69d92f9006d10e7e3e4871f5760823291ed8e1f (cherry picked from commit 8165cd3e0044896bed17be2c580d60bc93b4ed2b)