Specify is_fixed_read_only: true for net security mainline trunk stable flag

Mainline trunk stable flag must specify is_fixed_read_only: true since
server-side flags not supported for mainline in the trunk stable infrastructure
as of now.

Change-Id: Ibb2d599ee655f871f08b36bbc3cd6e286cf0d3c8
Test: TH
2 files changed