Revert "ANDROID: disable BLK_DEV_NBD for allmodconfig"

This reverts commit ca7dad50.

This re-enabled coverage of BLK_DEV_NBD. The clang-13 bug was worked
around in
commit 41e76c6a ("nbd: use shifts rather than multiplies")

Bug: 199191028
Link: https://github.com/ClangBuiltLinux/linux/issues/1438


Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: Ifcb6131e5c8b12e4c784320adac639b573198b1f