net: capture: Fix the return value of net_capture_is_enabled()

The net_capture_is_enabled() function returns boolean value
so fix the function prototype.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

include/net/capture.h

@@ -141,7 +141,7 @@ static inline bool net_capture_is_enabled(const struct device *dev)
 #else
 	ARG_UNUSED(dev);
 
-	return -ENOTSUP;
+	return false;
 #endif
 }