net: lwm2m: introduce input formatter private data

The JSON formatter is currently not enabled for incoming WRITE
operations.  To update the code in the formatter and not litter
the input context with extra data, let's allow formatters to
store their own user data.

Signed-off-by: Michael Scott <[email protected]>

Author: mike-scott

subsys/net/lib/lwm2m/lwm2m_object.h

@@ -282,6 +282,9 @@ struct lwm2m_input_context {
 
 	/* length of incoming opaque */
 	u16_t opaque_len;
+
+	/* private output data */
+	void *user_data;
 };
 
 /* Establish a message timeout callback */
@@ -408,6 +411,23 @@ engine_clear_out_user_data(struct lwm2m_output_context *out)
 	out->user_data = NULL;
 }
 
+static inline void engine_set_in_user_data(struct lwm2m_input_context *in,
+					   void *user_data)
+{
+	in->user_data = user_data;
+}
+
+static inline void *engine_get_in_user_data(struct lwm2m_input_context *in)
+{
+	return in->user_data;
+}
+
+static inline void
+engine_clear_in_user_data(struct lwm2m_input_context *in)
+{
+	in->user_data = NULL;
+}
+
 /* inline multi-format write / read functions */
 
 static inline size_t engine_put_begin(struct lwm2m_output_context *out,