Make sure symlinks created by ueventd are correctly labeled

Bug: 391078491
Test: `ls -alZ /dev/block/by-name | grep "boot_[ab]"` in cuttlefish.
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-23 13:03 boot_a -> /dev/block/vda2
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-23 13:03 boot_b -> /dev/block/vda3
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-23 13:03 init_boot_a -> /dev/block/vda4
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-23 13:03 init_boot_b -> /dev/block/vda5
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-23 13:03 vendor_boot_a -> /dev/block/vda6
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-23 13:03 vendor_boot_b -> /dev/block/vda7

Previously it was
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-21 13:36 boot_a -> /dev/block/vda2
lrwxrwxrwx 1 root root u:object_r:block_device:s0             15 2025-01-21 13:36 boot_b -> /dev/block/vda3
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-21 13:36 init_boot_a -> /dev/block/vda4
lrwxrwxrwx 1 root root u:object_r:block_device:s0             15 2025-01-21 13:36 init_boot_b -> /dev/block/vda5
lrwxrwxrwx 1 root root u:object_r:boot_block_device:s0        15 2025-01-23 13:03 vendor_boot_a -> /dev/block/vda6
lrwxrwxrwx 1 root root u:object_r:block_device:s0             15 2025-01-23 13:03 vendor_boot_b -> /dev/block/vda7

Change-Id: I448514cbf44f1f86c7f3493de23ede4690c7c4ac