Revert "ipacm: ignore removeDownstream request if netdev down"

This reverts commit b2c20467fe5158224a66d7f06d4ab078480f7d23.

Test: as follows
    - built
    - flashed
    - booted
    - VTS tests pass without a SIM card (modulo 2 tests)
Bug: 36682246
Bug: 64479437

Change-Id: I9c75979c4ac249f8c4783da4daad96f2a0f6c4e8
(cherry picked from commit 33f30f9b664de96d58ecbbb5831aae8d477badd1)
diff --git a/msm8998/ipacm/src/IPACM_OffloadManager.cpp b/msm8998/ipacm/src/IPACM_OffloadManager.cpp
index 04f6806..332abd5 100644
--- a/msm8998/ipacm/src/IPACM_OffloadManager.cpp
+++ b/msm8998/ipacm/src/IPACM_OffloadManager.cpp
@@ -226,8 +226,8 @@
 	IPACMDBG_H("removeDownstream name(%s), ip-family(%d) \n", downstream_name, prefix.fam);
 	if(ipa_get_if_index(downstream_name, &index))
 	{
-		IPACMERR("netdev(%s) already removed, ignored\n", downstream_name);
-		return SUCCESS;
+		IPACMERR("fail to get iface index.\n");
+		return FAIL_HARDWARE;
 	}
 
 	evt_data = (ipacm_event_ipahal_stream*)malloc(sizeof(ipacm_event_ipahal_stream));