Add new flag for Tethering w/ SoftApConfig

Old flag gantry flow was disabled due to being out of sync
(b/362407371). This change adds a new version of the same flag to
kickstart a new gantry flow.

Flag: com.android.net.flags.tethering_with_soft_ap_config

Bug: 216524590
Test: build
Change-Id: I50701582852c2077e7807ab2685e390f112fd029
4 files changed