Change the sync word of the telemetry packets

[mgm8]

Now, the sync. word of the downlink/uplink and beacon are the same (0x5D, 0xE6, 0x2A, 0x7E). To avoid misunderstandings and interference between the two links, we should change this sequence of one the transceivers.

[mgm8]

We have to perform further tests to confirm if this is necessary. Maybe the transfer rate difference is enough to avoid interference between the two communication links.