[sf] make legacy frontend debug flag persistent

Legacy frontend is still the default but we enable the new
front end, we want to disable the legacy by default as well.

Change-Id: I04ec50e05e9022be6efe1f83f29783ef49b11023
Test: presubmit
Bug: 238781169
(cherry picked from commit b999a7b415ca336270201b1ad346114769e91368)
1 file changed