packet ranges not very clearly explained

[iphydf]

Based on #762.

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@iphydf can we add some comments here to make it more clear?

c-toxcore/toxcore/Messenger.h

Lines 67 to 71 in fc0cc08

	/* All packets starting with a byte in this range can be used for anything. */
	#define PACKET_ID_LOSSLESS_RANGE_START 160
	#define PACKET_ID_LOSSLESS_RANGE_SIZE 32
	#define PACKET_LOSSY_AV_RESERVED 8 /* Number of lossy packet types at start of range reserved for A/V. */

LOSSLESS packets are 160-191
LOSSY packets are 192-??? (whats the max packet ID for this?)

but the first 8 packet ids are reserved for A/V:
192-199 --> reserved for A/V not useable by clients

c-toxcore/toxav/rtp.h

Lines 33 to 36 in fc0cc08

	enum {
	rtp_TypeAudio = 192,
	rtp_TypeVideo,
	};

rtp_TypeVideo should be hardcoded to 193 to make it clear (which we are about to do in the Video PRs)