Set call_ring.multiple to false.

bug:5757158
Change-Id: Iea6adbcaea1e6cc50bbe591e471bf136721d4c91
diff --git a/system.prop b/system.prop
index ef4edf6..a8df17e 100644
--- a/system.prop
+++ b/system.prop
@@ -5,3 +5,6 @@
 rild.libpath=/vendor/lib/libsec-ril.so
 rild.libargs=-d /dev/ttys0
 telephony.lteOnCdmaDevice=0
+
+# Ril sends only one RIL_UNSOL_CALL_RING, so set call_ring.multiple to false
+ro.telephony.call_ring.multiple=0