media: add libav default traces to warning

Default trace level is ERROR. In order to investigate
video decoding issues, I change it to WARNING
After stabilisation, we should reset it to ERROR.

Issue: #79686
Change-Id: I2e77e1759e46748ddbef6f6a60c6cba55c4d0a41

src/media/libav_utils.cpp

@@ -86,7 +86,7 @@ static void
 setAvLogLevel()
 {
     char* envvar = getenv(AVLOGLEVEL);
-    signed level = AV_LOG_ERROR;
+    signed level = AV_LOG_WARNING;
 
     if (envvar != nullptr) {
         if (not (std::istringstream(envvar) >> level))