Fix magic number in multiclient DMA test and document breaking default-deny change in PR description

Author: jackctj117

test/wh_test_multiclient.c

@@ -452,8 +452,12 @@ static int _testGlobalKeyDma(whClientContext* client1, whServerContext* server1,
 
     static whServerDmaAddrAllowList dmaAllowList = {0};
 
-    memcpy(keyData1, "GlobalDmaCacheTestKey123456!", 28);
-    memcpy(keyData2, "GlobalDmaExportTestKey12345!", 28);
+    memset(keyData1, 0, sizeof(keyData1));
+    memcpy(keyData1, "GlobalDmaCacheTestKey123456!",
+           sizeof("GlobalDmaCacheTestKey123456!") - 1);
+    memset(keyData2, 0, sizeof(keyData2));
+    memcpy(keyData2, "GlobalDmaExportTestKey12345!",
+           sizeof("GlobalDmaExportTestKey12345!") - 1);
     memset(outBuf, 0, sizeof(outBuf));
 
     /* Register DMA allow list for both servers */