Do not auto-downgrade WPA3->Transition mode if password too short

Hotspot security is auto-downgraded from WPA3->Transition mode if the
band is changed from 6Ghz -> 2.4/5GHz. However, Transition mode requires
a password of 8 chars or more, but WPA3 SAE does not. Avoid changing the
security type if the current password is less than 8 chars.

Flag: EXEMPT minor bugfix

Bug: 366452667
Test: atest WifiHotspotRepositoryTest
Change-Id: I1abadd59966e170b51899782746b9f14e33e6186