feat: increase NGC lossy custom packet size

[Green-Sky]

since toxcore places the responsibility to ensure the data does not get lost on the user (programmer), this can be seen as backwards compatible.

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This change is 

[iphydf]

Why 1000? Why is lossless larger?

[Green-Sky]

1. this is a draft, to get my point across :)
2. lossless packets are split into parts of 500
3. the point: during filetransfers for ngc experimentation i discovered that my home network equipment did not like the spam of small packets at all, it stayed in low power mode, and only woke up when i started a tcp download simultaneously or increased toxcores packet size
   1000 here is just and arbitrary number that was large enough for me. It made filetransfers 2x faster.
   i cant imagine being the only one that is going to come across this issue. besides, larger payload means less overhead per transmitted byte :)

[Green-Sky]

quote from https://www.libtorrent.org/utp.html

The other approach of picking a very conservative packet size, that would be very unlikely to get fragmented has the following drawbacks:

1. People on good, normal, networks will be penalized with a small packet size. Both in terms of router load but also bandwidth waste.
2. Software routers are typically not limited by the number of bytes they can route, but the number of packets. Small packets means more of them, and more load on software routers.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (9b3c108) 71.52% compared to head (15ee46d) 71.65%.

Files	Patch %	Lines
toxcore/group_chats.c	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2384      +/-   ##
==========================================
+ Coverage   71.52%   71.65%   +0.12%     
==========================================
  Files          75       75              
  Lines       25195    25200       +5     
==========================================
+ Hits        18020    18056      +36     
+ Misses       7175     7144      -31     

☔ View full report in Codecov by Sentry.
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[zoff99]

still same question why 1000 ?

since tox already uses 1400 for everything else.

c-toxcore/toxcore/tox.h

Line 297 in 24b5472

#define TOX_MAX_MESSAGE_LENGTH 1372

c-toxcore/toxcore/tox.h

Line 306 in 24b5472

#define TOX_MAX_CUSTOM_PACKET_SIZE 1373

c-toxcore/toxcore/onion.h

Line 37 in 24b5472

#define ONION_MAX_PACKET_SIZE 1400

c-toxcore/toxcore/net_crypto.h

Line 80 in 24b5472

#define MAX_CRYPTO_PACKET_SIZE (uint16_t)1400

1000 (and also 500) does not make any sense

[Green-Sky]

still same question why 1000 ?

Treat this pr as a proof of concept, until we decide how large exactly.

1. and 3. from my comment still apply feat: increase NGC lossy custom packet size #2384 (comment)