[framework] Add Unknown error code and java doc for subscriptionId.

Bug: 380868368
Test: compile

Change-Id: I04fe8db2a9354fb9546bca0cbe685eb98b356fa9
diff --git a/nfc/api/system-current.txt b/nfc/api/system-current.txt
index e97b15d..a9e7e63 100644
--- a/nfc/api/system-current.txt
+++ b/nfc/api/system-current.txt
@@ -250,6 +250,7 @@
     field @FlaggedApi("android.nfc.enable_card_emulation_euicc") public static final int SET_SUBSCRIPTION_ID_STATUS_FAILED_INVALID_SUBSCRIPTION_ID = 1; // 0x1
     field @FlaggedApi("android.nfc.enable_card_emulation_euicc") public static final int SET_SUBSCRIPTION_ID_STATUS_FAILED_NOT_SUPPORTED = 3; // 0x3
     field @FlaggedApi("android.nfc.enable_card_emulation_euicc") public static final int SET_SUBSCRIPTION_ID_STATUS_SUCCESS = 0; // 0x0
+    field @FlaggedApi("android.nfc.enable_card_emulation_euicc") public static final int SET_SUBSCRIPTION_ID_STATUS_UNKNOWN = -1; // 0xffffffff
   }
 
 }