Fix default network mode reset on sim1

On first boot when we try to set the default data sub network type,
the subscription controller tries to sync what's in the sim table and
what the preferred network mode is in the settings provider.

We read the user's mode for SIM 1 and set the preferred mode to that,
but on first boot it may be unset, setting the preferred mode to -1. We
should fall back to the current network mode if the user mode is unset.

Ref: CYNGNOS-1316

Change-Id: I0c7dec804965a7a4ada0acb34bfb1f511a65eb94
Signed-off-by: Roman Birg <roman@cyngn.com>