statd: also silence JSONDecodeError on check=False

In d616623a an attempt to silence bogus return values from mctl, when
multicast snooping is disabled on a bridge.  That helped get data back
for operational to produce `show interfaces` *with* a bridge and ports
but still emitted bogus log warnings.

This patch addresses that by checking 'check' on JSONDcodeError as well
before emitting any log error.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/statd/python/yanger/yanger.py

@@ -137,8 +137,9 @@ def run_json_cmd(cmd, testfile, default=None, check=True):
             return default
         raise
     except json.JSONDecodeError as err:
-        logger.error(f"failed parsing JSON output of command: {' '.join(cmd)}"
-                     f", error: {err}")
+        if check is True:
+            logger.error("failed parsing JSON output of command: "
+                         f"{' '.join(cmd)}, error: {err}")
         if default is not None:
             return default
         raise