Use com.android.vndk.current variant for vndk list

New linkerconfig reads some txt files which list various kinds of
vndk libraries. For example, vndksp.libraries.txt file has the list of
VNDKSP type libraries. The exact file names are retrieved from .vendor
variants.

With VNDK APEX, .vendor variants are not installed but
.com.android.vndk.current variants are packaged into VNDK APEX.

This CL changes the variant type from .vendor to
.com.android.vndk.current so that *.libraries.txt files can list the
installed files correctly.

Bug: 141451661
Test: m && device boot
Change-Id: Ibbc27b1ae6a44cc2337a0b14918caa27107a4c8e