pkg/build: copy android kernel to obj/vmlinux
pkg/build: copy android kernel to obj/vmlinux

Since it wasn't copied here, SyzCI would fail during image testing with

"failed to open ELF file: .../obj/vmlinux: ... no such file or
directory"

google/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller