I meant something like this (assuming no weird lengths like len=0 are to be received here):
```
switch (rtp_pl_len) {
case GSM_HR_BYTES_RTP_TS101318:
	/* Convert from TS 101 318 to RFC 5993 */
	if (OSMO_UNLIKELY(!ts101318 && rfc5993)) {
		msg = l1sap_msgb_alloc(rtp_pl_len + 1);
		if (!msg)
			return NULL;
		msgb_put_u8(msg, 0x00);
		memcpy(msgb_put(msg, rtp_pl_len), rtp_pl, rtp_pl_len);
		return msg;
	} 
	break; 
case GSM_HR_BYTES_RTP_RFC5993:
	/* Convert from RFC 5993 TS 101 318 */
	if (OSMO_UNLIKELY(!rfc5993 && ts101318)) {
		msg = l1sap_msgb_alloc(rtp_pl_len - 1);
		if (!msg)
			return NULL;
		memcpy(msgb_put(msg, rtp_pl_len - 1), rtp_pl + 1, rtp_pl_len - 1);
		return msg;
	}
	break;
default:
	OSMO_ASSERT(0);
}
	/* No conversion needed since the RTP payload is already in a supported format */
	msg = l1sap_msgb_alloc(rtp_pl_len);
	if (!msg)
		return NULL;
	memcpy(msgb_put(msg, rtp_pl_len), rtp_pl, rtp_pl_len);
```