dealing with RTP headerextensions

[fippo]

what is the best way to deal with RTP header extensions?

struct rtp_header {
  ...
  	struct {
		uint16_t type;  /**< Defined by profile     */
		uint16_t len;   /**< Number of 32-bit words */
	} x;

looks like there is some support but I would expect them to be part of the header and getting serialized and parsed by that but there is no support for encoding them in rtp_hdr_encode.

Adding some support shouldn't be too hard but I wonder about the right API.
For serialization maybe something along the lines of

rtp_hdrext_encode(struct mbuf *mb, uint16_t id, struct mbuf *mb, ...)

similar to stun_msg_encode?
This would then be done after calling rtp_hdr_encode

[fippo]

#591 addresses that, thank you @alfredh