Call getKernelLevel() only if kernel is GKI 2.0

Non-GKI or pre-S vendor wouldn't define kernel level, thus
getKernelLevel() would fail.
GKI 2.0 kernel release string format ensures getKernelLevel() to return
a valid value
https://source.android.com/devices/architecture/kernel/gki-versioning

Bug: 215380606
Test: atest vts_gki_compliance_test
Change-Id: I290d8c7a25dccacc47823c30d551ef530f70e002
1 file changed