selftests: userfaultfd skip if unavailable am: b63639e78f am: 609d8fab75 am: 535c74393f

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

Change-Id: I221e8c90fc7743507fb187a9fc478bd0ed34553f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>