Add flag to set call extra on incoming call for DSDA devices

- For DSDA or virtual DSDA enabled devices, when there is an incoming
  call on sub1 and an incoming call on SIM2: if either SIM does not
support hold capability, the existing call needs to be terminated.
- Setting this flag enables the above behavior.
- DSDS devices are not affected- if 2 simultaneous calls are received
  (eg. on WFC + WFC), the existing call will always be terminated.

Bug: 315993953
Test: Updated TelephonyConnectionServiceTests.
Change-Id: I08a4bd20d55448e15112361ffeff4e6143d32928
diff --git a/flags/ims.aconfig b/flags/ims.aconfig
index 92d003d..78f43dc 100644
--- a/flags/ims.aconfig
+++ b/flags/ims.aconfig
@@ -48,3 +48,10 @@
     description: "This flag is created to notify emergency registration state changed."
     bug:"312101946"
 }
+
+flag {
+    name: "call_extra_for_non_hold_supported_carriers"
+    namespace: "telephony"
+    description: "For DSDA devices, controls whether the existing call will be dropped when an incoming call on a different sub is answered, when either sub does not support hold capability."
+    bug:"315993953"
+}