Fix the DSU notification behavior

The 'mOneShot' should default to 'true' to prevent accidental activation of the sticky mode in the system.

Bug: 339788967
Test: adb shell am start-activity \
    -n com.android.dynsystem/com.android.dynsystem.VerificationActivity \
    -a android.os.image.action.START_INSTALL \
    -d file:///storage/emulated/0/Download/system.raw.gz \
    --el KEY_SYSTEM_SIZE $(du -b system.raw|cut -f1) \
    --el KEY_USERDATA_SIZE 4294967296

Change-Id: Iad40d9923fa0680f6e8f37690bed817af2a19f04