The code in `rtp_stop' checks for the sentinel value -1 when trying to
close sockets. Without this, it might get (and then ignore!) a spurious
`EBADF' when shutting down.
static int rtp_payload;
/** @brief RTP output socket */
static int rtp_payload;
/** @brief RTP output socket */
/** @brief RTP output socket (IPv6) */
static int rtp_fd6;
/** @brief RTP output socket (IPv6) */
static int rtp_fd6;
+/** @brief RTP unicast output socket (IPv6) */
+static int rtp_fd6 = -1;
/** @brief RTP SSRC */
static uint32_t rtp_id;
/** @brief RTP SSRC */
static uint32_t rtp_id;