ToneGenerator: fix dual sim ringback tone

If dual sim device has two SIM cards inserted,
in airplane mode it sets "gsm.operator.iso-country" prop
to a single comma, which prevents ToneGenerator to access
prop for "gsm.sim.operator.iso-country" - SIM provider
country code. When VoWifi is used to make a call,
incorrect ringback tone is being played (generic one),
instead if one being read from gsm.sim.operator.iso-country.

This patch fix this, and allows ToneGenerator to correctly
recognize SIM country code.

Bug: 65859291
Test: Check ringback tone during SIM2 VoWiFi in flight mode

Change-Id: Ibb57d38432f3d99f2eac568aec2a949af5e2a9cd