MAVLINK heartbeats from recent SIK firmware not detected

[syn-tax-err]

Recent versions of SIK use a different radio status message ID in MAVLINK, which is currently not detected by servald, causing new RFD radios to appear no-op (key symptom is "TX: 1, RX: 0" in the interface packet counters).

The relevant change in SIK is here:
ArduPilot/SiK@697c8a4#diff-9991bbe30c29719d7f8948c2d4fb3b56R47
TL;DR: new message 109 (0x6d) replaces old message 166 (0xa6), message format is unchanged.

Currently, servald only tests for old MAVLINK heartbeats, ignoring the new ones. This happens at two locations in the code:

serval-dna/radio_link.c

Line 55 in c252644

#define MAVLINK_MSG_ID_RADIO 166

serval-dna/radio_link.c

Lines 346 to 350 in c252644

	if (payload[0]==0xFE
	&& payload[1]==9
	&& payload[3]==RADIO_SOURCE_SYSTEM
	&& payload[4]==RADIO_SOURCE_COMPONENT
	&& payload[5]==MAVLINK_MSG_ID_RADIO){

serval-dna/radio_link.c

Lines 476 to 480 in c252644

	if (p[0]==0xFE
	&& p[1]==9
	&& p[3]==RADIO_SOURCE_SYSTEM
	&& p[4]==RADIO_SOURCE_COMPONENT
	&& p[5]==MAVLINK_MSG_ID_RADIO){

The issue is fixed by testing payload[5] against both message type IDs.