Log exceptions when querying MAC address as warnings

Querying of MAC addresses does not work on some devices or when it is in
certain states like fastboot.

Bug: 36140837
Change-Id: Id73063f9d649cb14ff1820279592df922f826a0a
diff --git a/src/com/android/tradefed/device/NativeDevice.java b/src/com/android/tradefed/device/NativeDevice.java
index 1e96ae5..85efae4 100644
--- a/src/com/android/tradefed/device/NativeDevice.java
+++ b/src/com/android/tradefed/device/NativeDevice.java
@@ -3710,7 +3710,7 @@
         } catch (IOException | TimeoutException | AdbCommandRejectedException |
                 ShellCommandUnresponsiveException e) {
             CLog.w("Failed to query MAC address for %s", mIDevice.getSerialNumber());
-            CLog.e(e);
+            CLog.w(e);
         }
         String output = receiver.getOutput().trim();
         if (isMacAddress(output)) {