selftests: userfaultfd skip if unavailable am: b63639e78f

Original change: https://android-review.googlesource.com/c/platform/external/linux-kselftest/+/2041084

Change-Id: I7ef30162be94f739b54c6f0b8d84dd1f62ddfc5e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>