+/**
+ * Send an AX25 frame on the channel.
+ * \param ctx AX25 context to operate on.
+ * \param dst the destination callsign for the frame, \see AX25_CALL
+ * for a handy way to create a callsign on the fly.
+ * \param src the source callsign for the frame, \see AX25_CALL
+ * for a handy way to create a callsign on the fly.
+ * \param _buf payload buffer.
+ * \param len length of the payload.
+ */